Nucleic acid amplification

ABSTRACT

Methods and compositions for the amplification of nucleic acids and generation of concatemers are disclosed. Amplification methods provided herein may be performed under isothermal conditions. Methods and compositions may include reagents such nucleic acid polymerases and primers.

CROSS-REFERENCE TO RELATED APPLICATIONS

This applications claims the benefit of, and priority to U.S. Provisional Patent Application No. 61/800,606, filed Mar. 15, 2013, the content of which is hereby incorporated by reference in its entirety for all purposes.

BACKGROUND

There is an increasing need for methods and reagents for the amplification of nucleic acids. Generation of multiple copies of a particular nucleic acid is often necessary or helpful in order for the nucleic acid to be used for a given application. For example, in order to analyze the nucleotide sequence of a nucleic acid of interest, frequently, the nucleic acid is replicated to increase its copy number before the sequence is analyzed. In another example, in order to determine the presence or absence of a particular nucleic acid in a sample, a sample may be treated under conditions such that if the particular nucleic acid is present in the sample, it may be amplified. In another example, a nucleic acid for use as probe may be copied repeatedly to generate a large number of nucleic acids containing the same sequence as the original nucleic acid template, thereby generating many copies of the nucleic acid which may be used as a probe.

A variety of methods for the amplification of nucleic acids are known. For example, polymerase chain reaction (“PCR”) (see, e.g. U.S. Pat. No. 4,683,202) is a popular method for the amplification of nucleic acids. To successfully perform a PCR reaction, the reaction must be performed at multiple different temperatures. This requires hardware or other mechanisms for repeatedly changing the temperature of the PCR reaction. Another method for amplification of nucleic acids is referred to as loop-mediated isothermal amplification (“LAMP”) (see, e.g. U.S. Pat. No. 6,410,278). LAMP reactions may be performed isothermally, but typically involve the use of four different primers which recognize a total of six distinct sequences on the target nucleic acid.

To facilitate the generation of amplified nucleic acids for the many and growing number of applications which use amplified nucleic acids, new methods and reagents for the amplification of nucleic acids are desired.

INCORPORATION BY REFERENCE

All publications, patents, and patent applications mentioned in this specification are herein incorporated by reference to the same extent as if each individual publication, patent, or patent application was specifically and individually indicated to be incorporated by reference.

SUMMARY

Provided herein are methods and compositions relating to the amplification of nucleic acids and the generation of concatemers.

In some embodiments, provided herein is a method for generating a concatemer comprising two or more copies of a double-stranded nucleic acid template, the method comprising: (A) treating a primary double-stranded nucleic acid comprising the double-stranded nucleic acid template with a first copy of a first primer and a polymerase under conditions such that an extension product of the first copy of the first primer is synthesized which is annealed to a first strand of the double-stranded nucleic acid template, wherein the first primer comprises a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising: (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and the template-binding region of the first copy of the first primer anneals to the first strand of the double-stranded nucleic acid template, (B) treating the extension product of the first copy of the first primer of step (A) with a second primer and a polymerase under conditions such that an extension product of the second primer is synthesized which is annealed to the extension product of the first copy of the first primer of step (A), wherein the second primer comprises a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, the tail region of the second primer contains a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer, if the sequences are aligned such that the 5′ terminal nucleotide of the second primer is aligned with the innermost nucleotide of the tail region of the first primer and the 5′ terminal nucleotide of the first primer is aligned with the innermost nucleotide of the tail region of the second primer, the template-binding region of the second primer anneals to the extension product of the first copy of the first primer of step (A), and the extension product of the second primer contains a 5′ terminal nucleotide, a 3′ terminal nucleotide, and a 3′ terminal region comprising the 3′ terminal nucleotide, wherein the 3′ terminal region contains the same nucleotide sequence as the nucleotide sequence of the tail region of the second primer read in the 5′ to 3′ direction, and the final nucleotide of the 3′ terminal region is the 3′ terminal nucleotide of the extension product of the second primer, (C) treating the extension product of the second primer of step (B) with a second copy of the first primer and a polymerase under conditions such that an extension product of the second copy of the first primer is synthesized which is annealed to the extension product of the second primer of step (B), to produce a first copy of a secondary nucleic acid comprising the extension product of the second primer of step (B) and the extension product of the second copy of the first primer, wherein the extension product of the second copy of the first primer contains a 5′ terminal nucleotide, a 3′ terminal nucleotide, and a 3′ terminal region comprising the 3′ terminal nucleotide, wherein the 3′ terminal region contains the same nucleotide sequence as the nucleotide sequence of the tail region of the first primer read in the 5′ to 3′ direction, and the final nucleotide of the 3′ terminal region is the 3′ terminal nucleotide of the extension product of the second primer, (D) repeating steps (A)-(C) one or more addition times to generate at least a second copy of the secondary nucleic acid of step (C), (E) treating the first copy of the secondary nucleic acid of step (C) and the second copy of the secondary nucleic acid of step (D) under conditions such that the 3′ terminal region of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid anneals to the 3′ terminal region of the extension product of the second primer of the second copy of the secondary nucleic acid, to produce a cross-over structure comprising the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid and the extension product of the second primer of the second copy of the secondary nucleic acid, (F) treating the cross-over structure of step (E) with a polymerase under conditions such that an extension product of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid is synthesized and an extension product of the extension product of the second primer of the second copy of the secondary nucleic acid is synthesized, to produce a concatemer comprising two copies of the double-stranded nucleic acid template of step (A), wherein the concatemer comprises the extension product of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid and the extension product of the extension product of the second primer of the second copy of the secondary nucleic acid.

In some embodiments, provided herein is a method for generating a concatemer comprising two or more copies of a polynucleotide template, the method comprising, (A) treating a primary nucleic acid comprising the polynucleotide template with a first copy of a first primer and a polymerase under conditions such that an extension product of the first copy of the first primer is synthesized which is annealed to the polynucleotide template, wherein the first primer comprises a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer, (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and the template-binding region of the first copy of the first primer anneals to the polynucleotide template, (B) treating the extension product of the first copy of the first primer of step (A) with a second primer and a polymerase under conditions such that an extension product of the second primer is synthesized which is annealed to the extension product of the first copy of the first primer of step (A), wherein the second primer comprises a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middles section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, the tail region of the second primer contains a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer, if the sequences are aligned such that the 5′ terminal nucleotide of the second primer is aligned with the innermost nucleotide of the tail region of the first primer and the 5′ terminal nucleotide of the first primer is aligned with the innermost nucleotide of the tail region of the second primer, the template-binding region of the second primer anneals to the extension product of the first copy of the first primer of step (A), and the extension product of the second primer contains a 5′ terminal nucleotide, a 3′ terminal nucleotide, and a 3′ terminal region comprising the 3′ terminal nucleotide, wherein the 3′ terminal region contains the same nucleotide sequence as the nucleotide sequence of the tail region of the second primer read in the 5′ to 3′ direction, and the final nucleotide of the 3′ terminal region is the 3′ terminal nucleotide of the extension product of the second primer, (C) treating the extension product of the second primer of step (B) with a second copy of the first primer and a polymerase under conditions such that an extension product of the second copy of the first primer is synthesized which is annealed to the extension product of the second primer of step (B), to produce a first copy of a secondary nucleic acid comprising the extension product of the second primer of step (B) and the extension product of the second copy of the first primer, wherein the extension product of the second copy of the first primer contains a 5′ terminal nucleotide, a 3′ terminal nucleotide, and a 3′ terminal region comprising the 3′ terminal nucleotide, wherein the 3′ terminal region contains the same nucleotide sequence as the nucleotide sequence of the tail region of the first primer read in the 5′ to 3′ direction, and the final nucleotide of the 3′ terminal region is the 3′ terminal nucleotide of the extension product of the second primer, (D) repeating steps (A)-(C) one or more addition times to generate at least a second copy of the secondary nucleic acid comprising the extension product of the second primer of step (B) and the extension product of the second copy of the first primer of step (C), (E) treating the first copy of the secondary nucleic acid of step (C) and the second copy of the secondary nucleic acid of step (D) under conditions such that the 3′ terminal region of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid anneals to the 3′ terminal region of the extension product of the second primer of the second copy of the secondary nucleic acid, to produce a cross-over structure comprising the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid and the extension product of the second primer of the second copy of the secondary nucleic acid, (F) treating the cross-over structure of step (E) with a polymerase under conditions such that an extension product of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid is synthesized and an extension product of the extension product of the second primer of the second copy of the secondary nucleic acid is synthesized, to produce a concatemer comprising two copies of the polynucleotide template of step (A), wherein the concatemer comprises the extension product of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid and the extension product of the extension product of the second primer of the second copy of the secondary nucleic acid. In some embodiments, the nucleic acid polymerase of step (A) is a DNA polymerase. In some embodiments, the nucleic acid polymerase of step (A) is a reverse transcriptase.

In some embodiments, provided herein is a method for generating a concatemer comprising two or more copies of a double-stranded nucleic acid template, the method comprising, (A) preparing a reaction mixture comprising: (i) a primary nucleic acid comprising the double-stranded nucleic acid template (ii) an isolated nucleic acid polymerase, (iii) a first primer comprising a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (a) a tail region comprising (1) the 5′ terminal nucleotide of the primer (2) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (3) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (b) a template-binding region comprising (1) the 3′ terminal nucleotide of the primer (2) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (3) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, wherein the template-binding region is complementary to a first strand of the nucleic acid template, (iv) a second primer comprising a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (a) a tail region comprising (1) the 5′ terminal nucleotide of the primer (2) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (3) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (b) a template-binding region comprising (1) the 3′ terminal nucleotide of the primer (2) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (3) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and wherein the template-binding region is complementary to a second strand of the nucleic acid template, and wherein the tail region of the second primer contains a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer, if the sequences are aligned such that the 5′ terminal nucleotide of the second primer is aligned with the innermost nucleotide of the tail region of the first primer and the 5′ terminal nucleotide of the first primer is aligned with the innermost nucleotide of the tail region of the second primer, and (B) incubating the reaction mixture for at least 1 minute.

In some embodiments, provided herein is a method for generating a concatemer comprising two or more copies of a polynucleotide template, the method comprising, (A) preparing a reaction mixture comprising: (i) a nucleic acid comprising the polynucleotide template (ii) an isolated nucleic acid polymerase, (iii) a first primer comprising a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (a) a tail region comprising (1) the 5′ terminal nucleotide of the primer (2) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (3) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (b) a template-binding region comprising (1) the 3′ terminal nucleotide of the primer (2) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (3) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and wherein the template-binding region is complementary to the polynucleotide template, (iv) a second primer comprising a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (a) a tail region comprising (1) the 5′ terminal nucleotide of the primer (2) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (3) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (b) a template-binding region comprising (1) the 3′ terminal nucleotide of the primer (2) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (3) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and wherein the template-binding region is complementary to a nucleotide sequence complementary to the polynucleotide template, and wherein the tail region of the second primer contains a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer, if the sequences of the primers are aligned such that the 5′ terminal nucleotide of the second primer is aligned with the innermost nucleotide of the tail region of the first primer and the 5′ terminal nucleotide of the first primer is aligned with the innermost nucleotide of the tail region of the second primer, and (B) incubating the reaction mixture for at least 1 minute.

In some embodiments, provided herein is a method for generating a concatemer comprising two or more copies of a double-stranded nucleic acid template, the method comprising incubating together a first copy and a second copy of a double-stranded nucleic acid molecule comprising the double-stranded nucleic acid template and a polymerase, wherein the double-stranded nucleic acid molecule comprises a first strand and a second strand, each containing a plurality of nucleotides, the first strand comprises a 5′ terminal nucleotide and a 3′ terminal nucleotide and contains the general format of regions in the 5′ to 3′ direction: A1-B-A2, the second strand comprises a 5′ terminal nucleotide and a 3′ terminal nucleotide and contains the general format of regions in the 5′ to 3′ direction: C1-D-C2, region B comprises the nucleotide sequence a first strand of the double-stranded nucleic acid template, region D comprises the nucleotide sequence of a second strand of the double-stranded nucleic acid template, in the double-stranded nucleic acid molecule, region A1 is annealed to C2, B is annealed to D, and A2 is annealed to C1, a cross-over structure comprising the first strand of the first copy of the double-stranded nucleic acid molecule and the second strand of the second copy of the double-stranded nucleic acid molecule is generated, wherein the A2 region of the first strand is annealed to the C2 region of the second strand, an extension product of the first strand of the cross-over structure is synthesized and an extension product of the second strand of the cross-over structure is synthesized, to produce a concatemer comprising the extension product of the first strand of the cross-over structure annealed to the extension product of the second strand of the cross-over structure, wherein the concatemer contains two copies of the double-stranded nucleic acid template.

In some embodiments, all of the steps of a method provided herein are performed at a temperature of no greater than 70, 65, 60, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, or 10 C. In some embodiments, some of the steps of a method provided herein are performed at a temperature of no greater than 70, 65, 60, 65, 60, 55, 50, 45, 40, 35, 30, 25, 20, 15, or 10 C.

In some embodiments, two or more steps of a method provided herein are performed simultaneously in the same reaction. In some embodiments, all of the steps of a method provided herein are performed simultaneously in the same reaction.

In some embodiments, in a method provided herein, a nucleic acid template is amplified at least 10, 100, 1000, 10,000, 100,000, or 1,000,000-fold within 5, 10, 15, 20, 30, 40, 50, 60, 70, 80, 90, 120, or 180 minutes of initiation of the method.

In some embodiments, provided herein is a vessel, comprising in fluid communication therein: (A) an isolated nucleic acid polymerase, (B) a nucleic acid template comprising at least a first strand, (C) a first primer comprising a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, wherein the template-binding region is complementary to a first strand of the nucleic acid template, and (D) a second primer comprising a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and wherein the template-binding region is complementary to a nucleotide sequence complementary to first strand of the nucleic acid template, and wherein the tail region of the second primer contains a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer, if the sequences of the primers are aligned such that the 5′ terminal nucleotide of the second primer is aligned with the innermost nucleotide of the tail region of the first primer and the 5′ terminal nucleotide of the first primer is aligned with the innermost nucleotide of the tail region of the second primer.

In some embodiments, provided herein is a kit for detecting a target nucleic acid of interest comprising at least a first strand, the kit comprising two or more fluidically isolated containers, the containers collectively comprising: (A) an isolated nucleic acid polymerase, (B) a first primer comprising a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, wherein the template-binding region is complementary to the first strand of the target nucleic acid, and (C) a second primer comprising a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and wherein the template-binding region is complementary to a nucleotide sequence complementary to the first strand of the target nucleic acid, and wherein the tail region of the second primer contains a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer, if the sequences of the primers are aligned such that the 5′ terminal nucleotide of the second primer is aligned with the innermost nucleotide of the tail region of the first primer and the 5′ terminal nucleotide of the first primer is aligned with the innermost nucleotide of the tail region of the second primer.

In some embodiments, a kit provided herein comprises the target nucleic acid of interest.

In some embodiments, a vessel or kit provided herein comprises a nucleic acid dye.

In some embodiments, in a vessel or kit provided herein comprising an isolated nucleic acid polymerase, the isolated nucleic acid polymerase is a DNA polymerase. In some embodiments, in a vessel or kit provided herein comprising an isolated nucleic acid polymerase, the isolated nucleic acid polymerase is a reverse transcriptase. In some embodiments, in a vessel or kit provided herein comprising an isolated nucleic acid polymerase, the vessel or kit comprises both a DNA polymerase and a reverse transcriptase.

In some embodiments, in a method, vessel, or kit provided herein comprising a nucleic acid polymerase, the nucleic acid polymerase has strand displacement activity.

In some embodiments, a method provided herein comprises treating one or more of the reaction components or steps of the method with a nucleic acid dye.

In some embodiments, in a method, vessel, or kit provided herein comprising a nucleic acid template, the template is a DNA molecule. In some embodiments, in a method, vessel, or kit provided herein comprising a nucleic acid template, the template is an RNA molecule.

In some embodiments, in a method, vessel, or kit provided herein comprising a first primer, the tail region of the first primer comprises at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides. In some embodiments, in a method, vessel, or kit provided herein comprising a first primer, the tail region of the first primer comprises no more than 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, or 60 nucleotides.

In some embodiments, in a method, vessel, or kit provided herein comprising a second primer, the tail region of the second primer comprises at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides. In some embodiments, in a method, vessel, or kit provided herein comprising a second primer, the tail region of the second primer comprises no more than 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, or 60 nucleotides.

In some embodiments, in a method, vessel, or kit provided herein comprising a first primer, the template-binding region of the first primer comprises at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides. In some embodiments, in a method, vessel, or kit provided herein comprising a first primer, the template-binding region of the first primer comprises no more than 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, or 60 nucleotides.

In some embodiments, in a method, vessel, or kit provided herein comprising a second primer, the template-binding region of the second primer comprises at least 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, or 20 nucleotides. In some embodiments, in a method, vessel, or kit provided herein comprising a second primer, the template-binding region of the second primer comprises no more than 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 30, 40, 50, or 60 nucleotides.

In some embodiments, in methods and compositions provided herein wherein an RNA molecule is the template molecule or primary nucleic acid, amplification of the template may refer to generation of copies of DNA strands corresponding to the RNA molecule.

In some embodiments, a method provided herein comprises measuring a fluorescent signal from an assay comprising the method.

In some embodiments, a nucleic acid ligase may be included with a method or composition provided herein. In some embodiments, a nucleic acid template may be amplified more rapidly with a method provided herein when a ligase is included in a reaction mixture for a method provided herein, as compared to if a nucleic acid ligase is not included in the reaction.

BRIEF DESCRIPTION OF THE DRAWINGS

In the drawings,

FIG. 1 is a general schematic of a method provided herein.

FIG. 2A shows nucleotide sequences of certain primers used with methods provided herein.

FIG. 2B is a graph depicting results from reactions performed according to a method provided herein.

FIGS. 3A and 3B shows nucleotide sequences of certain primers used with methods provided herein.

FIGS. 3C and 3D are graphs depicting results from reactions performed according to a method provided herein.

FIG. 4 is a graph depicting results from reactions performed according to a method provided herein.

FIG. 5 is a graph depicting results from reactions performed according to a method provided herein.

FIG. 6 is a graph depicting results from reactions performed according to a method provided herein.

FIG. 7 is a sequence alignment depicting the nucleotide sequences of products generated in reactions performed according to a method provided herein.

It is noted that the drawings and elements therein are not necessarily drawn to shape or scale. For example, the shape or scale of elements of the drawings may be simplified or modified for ease or clarity of presentation. It should further be understood that the drawings and elements therein are for exemplary illustrative purposes only, and not be construed as limiting in any way.

DETAILED DESCRIPTION

While the invention includes various modifications and alternative forms, specific embodiments thereof are shown by way of example in the drawings and will herein be described in detail. It should be understood, however, that there is no intent to limit the invention to the particular forms disclosed, but on the contrary, the invention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the claims.

In some embodiments, provided herein are methods and compositions relating to the amplification of nucleic acids and the generation of concatemers.

Generation of nucleic acid concatemers also amplifies the number of copies of the nucleic acid template/particular nucleic acid in the concatemer. Accordingly, references herein to methods and compositions for the generation of concatemers also applies to the amplification of nucleic acids, and vice versa.

As used herein, a “polynucleotide” refers to a polymeric chain containing two or more nucleotides. “Polynucleotides” includes primers, oligonucleotides, nucleic acid strands, etc. A polynucleotide may contain standard or non-standard nucleotides. Typically, a polynucleotide contains a 5′ phosphate at one terminus (“5′ terminus”) and a 3′ hydroxyl group at the other terminus (“3′ terminus) of the chain. The most 5′ nucleotide of a polynucleotide may be referred to herein as the “5′ terminal nucleotide” of the polynucleotide. The most 3′ nucleotide of a polynucleotide may be referred to herein as the “3′ terminal nucleotide” of the polynucleotide.

The term “downstream” as used herein in the context of a polynucleotide containing a 5′ terminal nucleotide and a 3′ terminal nucleotide refers to a position in the polynucleotide which is closer to the 3′ terminal nucleotide than a reference position in the polynucleotide. For example, in a primer having the sequence: 5′ ATAAGC 3′, the “G” is downstream from the “T” and all of the “A”s.

The term “upstream” as used herein in the context of a polynucleotide containing a 5′ terminal nucleotide and a 3′ terminal nucleotide, refers to a position in the polynucleotide which is closer to the 5′ terminal nucleotide than a reference position in the polynucleotide. For example, in a primer having the sequence: 5′ ATAAGC 3′, the “T” is upstream from the “G”, the “C”, and the two “A”s closest to the “G”.

As used herein, “nucleic acid” includes both DNA and RNA, including DNA and RNA containing non-standard nucleotides. A “nucleic acid” contains at least one polynucleotide (a “nucleic acid strand”). A “nucleic acid” may be single-stranded or double-stranded.

As used herein, a “concatemer” refers to a nucleic acid molecule which contains within it two or more copies of a particular nucleic acid, wherein the copies are linked in series. Within the concatemer, the copies of the particular nucleic acid may be linked directly to each other, or they may be indirectly linked (e.g. there may be nucleotides between the copies of the particular nucleic acid). In an example, the particular nucleic acid may be that of a double-stranded nucleic acid template, such that a concatemer may contain two or more copies of the double-stranded nucleic acid template. In another example, the particular nucleic acid may be that of a polynucleotide template, such that a concatemer may contain two or more copies of the polynucleotide template.

As used herein, a “target” nucleic acid or molecule refers to a nucleic acid of interest. A target nucleic acid/molecule may be of any type, including single-stranded or double stranded DNA or RNA (e.g. mRNA).

As used herein, “complementary” sequences refer to two nucleotide sequences which, when aligned anti-parallel to each other, contain multiple individual nucleotide bases which pair with each other. It is not necessary for every nucleotide base in two sequences to pair with each other for sequences to be considered “complementary”. Sequences may be considered complementary, for example, if at least 30%, 40%, 50%, 55%, 60%, 65%, 70%, 75%, 80%, 85%, 90%, 95%, 98%, 99%, or 100% of the nucleotide bases in two sequences pair with each other. In addition, sequences may still be considered “complementary” when the total lengths of the two sequences are significantly different from each other. For example, a primer of 15 nucleotides may be considered “complementary” to a longer polynucleotide containing hundreds of nucleotides if multiple individual nucleotide bases of the primer pair with nucleotide bases in the longer polynucleotide when the primer is aligned anti-parallel to a particular region of the longer polynucleotide.

As used herein, the term “isolated” as applied to proteins, nucleic acids, or other biomolecules refers to a molecule that has been purified or separated from a component of its naturally-occurring environment (e.g. a protein purified from a cell in which it was naturally produced). An “isolated” molecule may be in contact with other molecules (for example, as part of a reaction mixture). As used herein, “isolated” molecules also include recombinantly-produced proteins or nucleic acids which have an amino acid or nucleotide sequence which occurs naturally. “Isolated” nucleic acids include polypeptide-encoding nucleic acid molecules contained in cells that ordinarily express the polypeptide where, for example, the nucleic acid molecule is at a chromosomal location different from that of natural cells. In some embodiments, “isolated” polypeptides are purified to at least 50%, 60%, 70%, 80%, 90%, 95%, 98%, or 100% homogeneity as evidenced by SDS-PAGE of the polypeptides followed by Coomassie blue, silver, or other protein staining method.

As used herein, a nucleic acid molecule which is described as containing the “sequence” of a template or other nucleic acid may also be considered to contain the template or other nucleic acid itself (e.g. a molecule which is described as containing the sequence of a template may also be described as containing the template), unless the context clearly dictates otherwise.

Embodiments of methods and compositions provided herein may be described with reference to FIG. 1. A primary nucleic acid 101 may be provided (FIG. 1A). The primary nucleic acid 101 may contain the sequence of a nucleic acid template 102. The nucleic acid template 102 may be a double-stranded nucleic acid containing a first strand 103 and a second strand 104. In FIG. 1, the first strand 103 of the double-stranded nucleic acid template has an exemplary nucleotide sequence in the 5′ to 3′ direction of: AACG+++GCTC, where +++ is any number and sequence of nucleotides. The first strand 103 also contains a 5′ terminal nucleotide (the 5′-most A) and a 3′ terminal nucleotide (the 3′-most C). The second strand 104 has an exemplary nucleotide sequence in the 5′ to 3′ direction of: GAGC˜˜˜CGTT, where ˜˜˜ is the same number of nucleotides and is complementary to +++. The second strand 104 also contains a 5′ terminal nucleotide (the 5′-most G) and a 3′ terminal nucleotide (the 3′-most T).

A first primer 105 and a second primer 106 may also be provided (FIG. 1B). In FIG. 1, the first primer 105 has an exemplary nucleotide sequence in the 5′ to 3′ direction of: ATGGGAGC. The first primer also contains a 5′ terminal nucleotide (the 5′-most A) and a 3′ terminal nucleotide (the 3′-most C). The second primer 106 has an exemplary nucleotide sequence in the 5′ to 3′ direction of: CCATAACG. The second primer also contains a 5′ terminal nucleotide (the 5′-most C) and a 3′ terminal nucleotide (the 3′-most G).

The first primer 105 may comprise two regions: i) a tail region and ii) a template-binding region (“temp” region). The tail region of the first primer 105 may contain three components: a) the 5′ terminal nucleotide of the primer, b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide, and c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides. In FIG. 1, the tail region of the first primer 105 has an exemplary nucleotide sequence in the 5′ to 3′ direction of: ATGG, of which the 5′ terminal nucleotide of the primer is the A, the middle section is the middle TG, and the innermost nucleotide is the 3′-most G. The template-binding region of the first primer 105 may contain three components: a) the 3′ terminal nucleotide of the primer, b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide, and c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides. In FIG. 1, the template-binding region of the first primer 105 has an exemplary nucleotide sequence in the 5′ to 3′ direction of: GAGC, of which the 3′ terminal nucleotide of the primer is the C, the middle section is the middle AG, and the innermost nucleotide is the 5′-most G.

The second primer 106 may comprise two regions: i) a tail region and ii) a template-binding region. The tail region of the first primer 106 may contain three components: a) the 5′ terminal nucleotide of the primer, b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide, and c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides. In FIG. 1, the tail region of the second primer 106 has an exemplary nucleotide sequence in the 5′ to 3′ direction of: CCAT, of which the 5′ terminal nucleotide of the primer is the 5′-most C, the middle section is the middle CA, and the innermost nucleotide is the T. The template-binding region of the second primer 106 may contain three components: a) the 3′ terminal nucleotide of the primer, b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide, and c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides. In FIG. 1, the template-binding region of the second primer 106 has an exemplary nucleotide sequence in the 5′ to 3′ direction of: AACG, of which the 3′ terminal nucleotide of the primer is the G, the middle section is the middle AC, and the innermost nucleotide is the 5′-most A.

In some embodiments, the tail region of the second primer may contain a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer, if the sequences of the primers are aligned such that the 5′ terminal nucleotide of the second primer is aligned with the innermost nucleotide of the tail region of the first primer and the 5′ terminal nucleotide of the first primer is aligned with the innermost nucleotide of the tail region of the second primer. For example, in FIG. 1, the tail region of the second primer 106 has a nucleotide sequence in the 5′ to 3′ direction of CCAT, and the tail region of the first primer 105 has a nucleotide sequence in the 5′ to 3′ direction of ATGG. These sequences are complementary when the 5′ terminal nucleotide of the second primer (C) is aligned with the innermost nucleotide of the tail region of the first primer (G) and the 5′ terminal nucleotide of the first primer (A) is aligned with the innermost nucleotide of the tail region of the second primer (T) 107 (FIG. 1B).

It should be noted that although the tail region of the second primer may contain a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer, typically, products formed by the annealing of the first primer and second primer are not desirable or useful for methods or compositions provided herein. Accordingly, in some embodiments, steps may be taken to minimize the formation of first primer-second primer annealed products. Such steps may include, for example, not pre-incubating a first primer and a second primer under conditions where the primers may anneal for an extended period of time before initiating a method provided herein.

The primary nucleic acid 101 may be treated with a first copy of the first primer 105 a and a polymerase 108 under conditions such that the template-binding region of the first copy of the first primer 105 a anneals to the first strand of the nucleic acid template 103 (FIG. 1C) and an extension product of the first copy of the first primer 111 is formed (FIG. 1D). The polymerase 108 may catalyze the formation of the extension product of the first copy of the first primer 111. The polymerase may have strand displacement activity. During the synthesis of the extension product of the first copy of the first primer 111, the polymerase may displace the second strand of the nucleic acid template 104 from the first strand of the nucleic acid template 103. Typically, the extension product is generated from the 3′ end of the first copy of the first primer 105 a. During the generation of the extension product of the first copy of the first primer 111, the first copy of the first primer 105 a may be covalently linked to the synthesized extension product, such that the first copy of the first primer becomes part of the molecule described herein as the “extension product of the first copy of the first primer”. The extension product of the first copy of the first primer 111 is complementary to the first strand of the nucleic acid template 103. In some embodiments, when the first copy of the first primer 105 a anneals to the first strand of the nucleic acid template 103, the template-binding region but not the tail region of the first copy of the first primer 105 a anneals to the first strand of the nucleic acid template.

In some embodiments, conditions such that the template-binding region of the first copy of the first primer 105 a anneals to the first strand of the nucleic acid template 103 and an extension product of the first copy of the first primer 111 is formed may include any condition sufficient to support polymerase-based nucleic acid synthesis. Example conditions for polymerase-based nucleic acid synthesis are known in the art and are provided, for example, in Molecular Cloning: A Laboratory Manual, M. R. Green and J. Sambrook, Cold Spring Harbor Laboratory Press (2012), which is herein incorporated by reference in its entirety.

The extension product of the first copy of the first primer 111 may be treated with the second primer 106 and a polymerase 108 under conditions such that the template-binding region of the second primer 106 anneals to the extension product of the first copy of the first primer 111 (FIG. 1E) and an extension product of the second primer 112 is formed (FIG. 1F). The polymerase 108 may catalyze the formation of the extension product of the second primer 106. The polymerase may have strand displacement activity. The polymerase may be the same type of polymerase as is used to generate an extension product of the first copy of the first primer 111, or it may be different. During the synthesis of the extension product of the second primer 112, the polymerase may displace the first strand of the nucleic acid template 103 from the extension product of the first copy of the first primer 111. Typically, the extension product is generated from the 3′ end of the second primer 106. During the generation of the extension product of the second primer 112, the second primer 106 may be covalently linked to the synthesized extension product, such that the second primer becomes part of the molecule described herein as the “extension product of the second primer”. The extension product of the second primer 112 is complementary to the extension product of the first copy of the first primer 111. In some embodiments, when the second primer 106 anneals to the extension product of the first copy of the first primer 111, the template-binding region but not the tail region of the second primer 106 anneals to the extension product of the first copy of the first primer 111. The extension product of the second primer 112 contains a 5′ terminal nucleotide, a 3′ terminal nucleotide, and a 3′ terminal region. The final nucleotide of the 3′ terminal region (T) is the 3′ terminal nucleotide of the extension product of the second primer (T), and the 3′ terminal region contains the same nucleotide sequence as the nucleotide sequence of the tail region of the second primer read in the 5′ to 3′ direction (CCAT).

In some embodiments, conditions such that the template-binding region of the second primer 106 anneals to the extension product of the first copy of the first primer 111 and an extension product of the second primer 112 is formed may include any condition sufficient to support polymerase-based nucleic acid synthesis, including any condition discussed elsewhere herein. The conditions may be the same as used to generate an extension product of the first copy of the first primer 111, or they may be different.

The extension product of the second primer 112 may be treated with a second copy of the first primer 105 b and a polymerase 108 under conditions such that the template-binding region of the second copy of the first primer 105 b anneals to the extension product of the second primer 112 (FIG. 1G) and an extension product of the second copy of the first primer 113 is formed (FIG. 1F). The polymerase 108 may catalyze the formation of the extension product of the second copy of the first primer 113. The polymerase may have strand displacement activity. The polymerase may be the same type of polymerase as is used to generate an extension product of the first copy of the first primer 111 or an extension product of the second primer 112, or it may be different. During the synthesis of the extension product of the second copy of the first primer 113, the polymerase may displace the extension product of the first copy of the first primer 111 from the extension product of the second primer 112. Typically, the extension product is generated from the 3′ end of the first copy of the first primer 105 b. During the generation of the extension product of the second copy of the first primer 113, the second copy of the first primer 105 b may be covalently linked to the synthesized extension product, such that the second copy of the first primer becomes part of the molecule described herein as the “extension product of the second copy of the first primer”. The extension product of the second copy of the first primer 113 is complementary to the extension product of the second primer 112. In some embodiments, when the first copy of the first primer 105 b anneals to the extension product of the second primer 112, both the template-binding region and the tail region of the second copy of the first primer 105 b anneals to the extension product of the second primer 112. The extension product of the second copy of the first primer 113 contains a 5′ terminal nucleotide, a 3′ terminal nucleotide, and a 3′ terminal region. The final nucleotide of the 3′ terminal region (G) is the 3′ terminal nucleotide of the extension product of the second primer (G), and the 3′ terminal region contains the same nucleotide sequence as the nucleotide sequence of the tail region of the first primer read in the 5′ to 3′ direction (ATGG).

In some embodiments, conditions such that the template-binding region of the second copy of the first primer 105 b anneals to the extension product of the second primer 112 and an extension product of the second copy of the first primer 113 is formed may include any condition sufficient to support polymerase-based nucleic acid synthesis, including any condition discussed elsewhere herein. The conditions may be the same as used to generate an extension product of the first copy of the first primer 111 or an extension product of the second primer 112, or they may be different.

Generation of the extension product of the second copy of the first primer 113 may result in the generation of a molecule comprising the extension product of the second copy of the first primer 113 and the extension product of the second primer 112, which may be referred to herein as the “secondary nucleic acid” 115. Within the secondary nucleic acid 115, the extension product of the second copy of the first primer 113 may be annealed to the extension product of the second primer 112. In addition, the secondary nucleic acid 115 contains the sequence of the nucleic acid template 102. The secondary nucleic acid 115 has a greater nucleotide length than the nucleic acid template 102 alone, as in addition to the sequence of the nucleic acid template 102, it may include the sequence of the tail regions of the first primer and the second primer, and complementary sequences thereof. Specifically, a secondary nucleic acid 115 may have a first end region 116 and a second end region 117. The first end region 116 may comprise the 3′ terminal region of the extension product of the second primer 112, and the complement thereof. The second end region 117 may comprise the 3′ terminal region of the extension product of the second copy of the first primer 113, and the complement thereof.

A first copy 115 a and a second copy 115 b of the secondary nucleic acid 115 may be provided (FIG. 1I). The first copy 115 a and second copy 115 b of the secondary nucleic acid 115 may be generated by any process whereby a nucleic acid having the general structure of the secondary nucleic acid 115 may be generated, including any process discussed elsewhere herein. For example, the full process as described above for generating a secondary nucleic acid 115 from a primary nucleic acid 101 may be repeated two times, in order to generate the first copy 115 a and the second copy 115 b of the secondary nucleic acid. In another example, the first copy 115 a and the second copy 115 b of the secondary nucleic acid may be generated from a single copy of an extension product of a first copy of first primer 111. In this example, two copies 112 a, 112 b of an extension product of the second primer may be generated from the single copy of the extension product of a first copy of a first primer 111, which may occur if a first copy of the extension product of the second primer 112 a is displaced from the single copy of the extension product of the first copy of the first primer 111, thereby permitting the generation of a second copy of the extension product of the second primer 112 a from the single copy of the extension product of a first copy of a first primer 111. Then, for example, an extension product of the second copy of the first primer 113 a, 113 b may be generated from each copy of the extension product of the second primer 112 a, 112 b, respectively.

The first copy 115 a and second copy 115 b of the secondary nucleic acid may be treated under conditions such that the 3′ terminal region of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid 113 a anneals to the 3′ terminal region of the extension product of the second primer of the second copy of the secondary nucleic acid 112 b, to produce a cross-over structure 117 comprising these strands (FIG. 1J) (for simplicity, strands 113 b and 112 a are not shown). The cross-over structure 117 may be further treated with a polymerase under conditions such that extension products of both component strands 112 b, 113 a are formed, the extension products which may be referred to herein as a “first concatemer strand” 121 and a “second concatemer strand” 122, respectively. The first concatemer strand 121 and the second concatemer strand 122 may be annealed together, and may be collectively referred to as a concatemer 120 (FIG. 1K). The concatemer 120 may contain two or more copies of the nucleic acid template 102. Within the concatemer 120, some or all of the two or more copies of the nucleic acid template 102 may be separated from each other by the sequences of the tail regions of the first primer 105 and second primer 106, where the sequences of the tail regions are annealed to each other. For example, in the concatemer 120 of FIG. 1K, the first copy of the first strand of the double-stranded nucleic acid template is separated from the second copy of the first strand of the double-stranded nucleic acid template by the sequence, in 5′-3′ order: CCAT. CCAT is also the sequence, in 5′-3′ order, of the tail region of the second primer 106. Similarly, in the concatemer 120 of FIG. 1K, the first copy of the second strand of the double-stranded nucleic acid template is separated from the second copy of the second strand of the double-stranded nucleic acid template by the sequence, in 5′-3′ order: ATGG. ATGG is also the sequence, in 5′-3′ order, of the tail region of the first primer 105. Within the concatemer, the CCAT of the first concatemer strand is annealed to the ATGG of the second concatemer strand.

In some embodiments, conditions such that a cross-over structure 117 or extension products of the strands of a cross-over structure are formed may include any condition sufficient to support polymerase-based nucleic acid synthesis, including any condition discussed elsewhere herein. The conditions may be the same as used to generate an extension product of the first copy of the first primer 111, an extension product of the second primer 112, or an extension product of the second copy of the first primer 111, or they may be different.

In some embodiments, concatemers provided herein may further increase in length according to the process generally outlined in FIG. 1I-1K. For example, two of the concatemer molecules 120 as shown in FIG. 1K may be treated such that they form a cross-over structure similar to than in FIG. 1J (except with longer strands), followed by a larger concatemer molecule containing four copies of the nucleic acid template 102. In another example, a secondary nucleic acid 115 and a concatemer 120 may form a cross-over structure, followed by a larger concatemer molecule containing three copies of the nucleic acid template 102. In some embodiments, in methods provided herein, multiple different concatemers of multiple different lengths may be simultaneously generated.

Concatemers generated according to methods and compositions provided herein may be of any length of nucleotides. In some embodiments, concatemer molecules generated herein may be at least 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10,000, 15,000, 20,000, or 25,000 nucleotides in length. In some embodiments, concatemer molecules generated herein may be no more than 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10,000, 15,000, 20,000, or 25,000 nucleotides in length. In some embodiments, concatemer molecules generated herein may have a length selected from a range having a minimum value of 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10,000, 15,000, or 20,000 nucleotides in length, and a maximum value of 40, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 400, 500, 600, 700, 800, 900, 1000, 1500, 2000, 3000, 4000, 5000, 6000, 7000, 8000, 9000, 10,000, 15,000, 20,000, or 25,000 nucleotides in length. In some embodiments, at least some concatemers generated according to a method or composition provided herein have characteristics described above. In some embodiments, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of concatemers generated according to a method or composition provided herein have characteristics described above.

Concatemers generated according to methods and compositions provided herein may contain any number of copies of a nucleic acid template/particular nucleic acid. In some embodiments, concatemer molecules generated herein may contain at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, or 100 copies of a nucleic acid template/particular nucleic acid. In some embodiments, concatemer molecules generated herein may contain no more than 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, or 100 copies of a nucleic acid template/particular nucleic acid. In some embodiments, concatemer molecules generated herein may have a number of copies of a nucleic acid template/particular nucleic acid selected from a range having a minimum value of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, or 90 copies, and a maximum value of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, or 100 copies. In some embodiments, at least some concatemers generated according to a method or composition provided herein have characteristics described above. In some embodiments, at least 10%, 20%, 30%, 40%, 50%, 60%, 70%, 80%, 90%, or 95% of concatemers generated according to a method or composition provided herein have characteristics described above.

Detection of Reactions

Progress of a method provided herein may be monitored in multiple different ways. In one embodiment, a reaction may be assayed for a nucleic acid amplification product (e.g. for the level of the product or the rate of its generation). In another embodiment, a reaction may be assayed for the activity of a polymerase along a nucleic acid template (e.g. for movement of a polymerase along a template strand). Thus, in some embodiments, events of a method provided herein may observed due to the accumulation of product from a method (which may be during or after completion of steps of the method), or due to detectable events occurring during the steps of a method.

The presence of amplified nucleic acids can be assayed, for example, by detection of reaction products (amplified nucleic acids or reaction by-products) or by detection of probes associated with the reaction progress.

In some embodiments, reaction products may be identified by staining the products with a dye. In some embodiments, a dye may have greater fluorescence when bound to a nucleic acid than when not bound to a nucleic acid. In some embodiments, a dye may intercalate with a double-stranded nucleic acid or it may bind to an external region of a nucleic acid. Nucleic acid dyes that may be used with methods and compositions provided herein include, for example, cyanine dyes, PicoGreen®, OliGreen®, RiboGreen®, SYBR® dyes, SYBR® Gold, SYBR® Green I, SYBR® Green II, ethidium bromide, dihydroethidium, BlueView™, TOTO® dyes, TO-PRO® dyes, POPO® dyes, YOYO® dyes, BOBO® dyes, JOJO® dyes, LOLO® dyes, SYTOX® dyes, SYTO® dyes, propidium iodide, hexidium iodide, methylene blue, DAPI, acridine orange, quinacrine, acridine dimers, 9-amino-6-chloro-2-methoxyacridine, bisbenzimide dyes, Hoechst dyes, 7-aminoactinomycin D, actinomycin D, hydroxystilbamidine, pyronin Y, Diamond™ dye, GelRed™, GelGreen™ and LDS 751.

In some embodiments, reaction products may be identified by analysis of turbidity of amplification reactions [or example, where increased turbidity is correlated with formation of reaction products and reaction by-products (e.g. pyrophosphate complexed with magnesium)].

In some embodiments, reaction products may be identified by separating a reaction performed according to a method herein by gel electrophoresis, followed by staining of the gel with a dye for nucleic acids. The dye may be any nucleic acid dye disclosed herein or otherwise known in the art.

In some embodiments, any method or composition known in the art for the detection of nucleic acids or processes associated with the generation of nucleic acids may be used with methods and compositions provided herein.

In some embodiments, a nucleic acid probe which contains a nucleotide sequence complementary to a portion of a nucleic acid template strand (or strand having a similar or identical sequence) and which contains one or both of a fluorescent reporter (fluorophore) and a quencher are included in a reaction provided herein.

In an example, a nucleic acid probe may contain a fluorescent reporter at its 5′ or 3′ terminus, and a quencher at the other terminus. The probe may further have a nucleotide sequence containing, in order, at least a first, second, and third region, where the first and third regions are complementary to each other, and where at least a portion of the second region is complementary to a portion of a strand of the nucleic acid template (the probe “detection sequence”). In some embodiments, the length of the second region may be greater than the length of the first or third regions. In some embodiments, the length of the second region may be between 10 and 40 nucleotides, and the length of first and third regions may be between 4 and 10 nucleotides. The probe may have at least two different conformations: (A) a conformation where the probe is not annealed to its detection sequence and where the first and third regions are annealed to each other; this conformation may be a “stem-loop” structure, where the first and third regions form the stem and the second region forms the loop, and (B) a conformation where the probe is annealed to its detection sequence; in this conformation, the second region or a portion thereof is annealed to its detection sequence and the first and third regions are not annealed to each other. In conformation (A) of the probe, the fluorescent reporter and quencher (which are located at opposite termini of the probe/at the outer ends of the first and third regions) may be in close proximity to each other (both being at the end of the stem structure formed by the annealing of the first and third regions), such that the fluorescent reporter is quenched. In conformation (B) of the probe, the fluorescent reporter and quencher may not be in close proximity to each other, such that the fluorescent reporter is not quenched. The probe may be used to monitor accumulation of a selected reaction product, for example, under reaction conditions where the probe may either form a stem-loop structure or anneal to its detection sequence. In some embodiments, if the detection sequence is present, the probe may anneal to the detection sequence, and the probe may fluoresce in response to light of a wavelength of the fluorphore's excitation spectrum. In contrast, if the detection sequence is not present, the probe may form a stem-loop structure, and not fluoresce in response to light of a wavelength of the fluorphore's excitation spectrum.

In another example, a nucleic acid probe may contain a fluorescent reporter at its 5′ or 3′ terminus, and it may be annealed to a nucleic acid primer containing a quencher. The nucleic acid primer containing a quencher may contain the quencher at a position in the primer such that when the nucleic acid probe is annealed to the primer, the fluorescent reporter is quenched. The probe may be used to monitor accumulation of a selected reaction product, for example, under reaction conditions where the probe may either anneal to the primer or anneal to its detection sequence. In some embodiments, if the detection sequence is present, the probe may anneal to the detection sequence, and the probe may fluoresce in response to light of a wavelength of the fluorphore's excitation spectrum. In contrast, if the detection sequence is not present, the probe may remain paired with the primer, and not fluoresce in response to light of a wavelength of the fluorphore's excitation spectrum.

In probes containing a fluorescent reporter and quencher pair, the fluorescent reporter and quencher may be selected so that the quencher can effectively quench the reporter. In some embodiments, a fluorescent reporter is paired with a quencher where the emission maximum of the fluorescent reporter is similar to the absorption maximum of the quencher. Fluorphores that may be used as the fluorescent reporter include, for example, CAL Fluor Gold, CAL Fluor Orange, Quasar 570, CAL Fluor Red 590, CAL Fluor Red 610, CAL Fluor Red 610, CAL Fluor Red 635, Quasar 670 (Biosearch Technologies), VIC, NED (Life Technologies), Cy3, Cy5, Cy5.5 (GE Healthcare Life Sciences), Oyster 556, Oyster 645 (Integrated DNA Technologies), LC red 610, LC red 610, LC red 640, LC red 670, LC red 705 (Roche Applies Science), Texas red, FAM, TET, HEX, JOE, TMR, and ROX. Quenchers that may be used include, for example, DDQ-I, DDQ-II (Eurogentec), Eclipse (Epoch Biosciences), Iowa Black FQ, Iowa Black RQ (Integrated DNA Technologies), BHQ-1, BHQ-2, BHQ-3 (Biosearch Technologies), QSY-7, QSY-21 (Molecular Probes), and Dabcyl.

In some embodiments, a method provided herein may be monitored in an apparatus containing a light source and an optical sensor. In some situations, the reaction may be positioned in the path of light from the light source, and light absorbed by the sample (e.g. in the case of a turbid reaction), scattered by the sample (e.g. in the case of a turbid reaction), or emitted by the sample (e.g. in the case of a reaction containing a fluorescent molecule) may be measured. In some embodiments, a method provided herein may be performed or monitored in a device or module therein as disclosed in U.S. patent application Ser. No. 13/769,779, filed Feb. 18, 2013, which is herein incorporated by reference in its entirety.

Using methods provided herein, specific amplification products of a nucleic acid template of interest may be identified within, for example, 30 seconds, 1 minute, 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 45 minutes, 60 minutes, 90 minutes, 120 minutes, 180 minutes, or 240 minutes of initiation of an amplification reaction. In other examples, using methods provided herein, amplification reactions which are positive for a nucleic acid template of interest may be identified when as few as 10, 50, 100, 500, 1000, 5000, 10,000, 50,000, 100,000, 500,000, or 1,000,000 copies of the template are generated. In other examples, using methods provided herein, the presence of a nucleic acid template of interest in a sample containing as few as 1, 2, 3, 4, 5, 10, 15, 20, 25, 30, 40, 50, 100, 200, 500, 1000, 5000, or 10,000 copies of the template of interest may be identified.

Methods provided herein may be performed for any length of time. Typically, the method will be performed for a length of time sufficient to monitor, for example, the rate of nucleic acid replication, the occurrence of polymerase activity, or the accumulation of amplification product. In some embodiments, a method provided herein may be performed for a total of less than 10 seconds, 30 seconds, 1 minute, 5 minutes, 10 minutes, 20 minutes, 30 minutes, 45 minutes, 1 hour, 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 12 hours, 16 hours, or 24 hours, by which time the rate of nucleic acid replication, the occurrence of polymerase activity, or the accumulation of amplification product was measured.

Methods provided herein may be terminated in various ways. In one embodiment, steps of a method may end upon the reduction in concentration or complete consumption of one or more reagents involved in one or more steps of the method (e.g. dNTPs). In another embodiment, steps of a method may end upon inactivation of one or more enzymes involved in one or more steps of the method (e.g. polymerases). Enzymes may be inactivated by various ways. For example, enzymes may gradually lose enzymatic activity over time due to random events that affect the structure of the enzyme, or enzymes may be exposed to a condition to accelerate the inactivation of the enzyme activity (e.g. high heat, extreme pH, etc.).

In some embodiments, a primary nucleic acid may be single stranded or double-stranded. A single stranded primary nucleic acid may also be referred to herein as a “primary polynucleotide”. A primary nucleic acid may be linear or circular. A primary nucleic acid may comprise a nucleic acid template. In some embodiments, the entirety of a primary nucleic acid may be a nucleic acid template. In other embodiments, a primary nucleic acid may contain one or more nucleotides which are not part of a nucleic acid template (e.g. the primary nucleic acid may be of a greater length than a nucleic acid template contained within the primary nucleic acid). In some embodiments, a primary nucleic acid may contain two or more copies of a nucleic acid template. A primary nucleic acid may contain DNA, RNA, or a mixture thereof. A linear primary nucleic acid may have blunt ends or sticky ends.

A primary nucleic acid may be of any length of nucleotides. For example, a primary nucleic acid may be at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length. In another example, a primary nucleic acid may be between 2 and 100,000, between 5 and 100,000, between 10 and 100,000, between 15 and 100,000, between 20 and 100,000, between 25 and 100,000, between 30 and 100,000, between 50 and 100,000, between 70 and 100,000, between 100 and 100,000, between 200 and 100,000, between 2 and 10,000, between 5 and 10,000, between 10 and 10,000, between 15 and 10,000, between 20 and 10,000, between 25 and 10,000, between 30 and 10,000, between 50 and 10,000, between 70 and 10,000, between 100 and 10,000, between 200 and 10,000, between 2 and 5,000, between 5 and 5,000, between 10 and 5,000, between 15 and 5,000, between 20 and 5,000, between 25 and 5,000, between 30 and 5,000, between 50 and 5,000, between 70 and 5,000, between 100 and 5,000, between 200 and 5,000, between 2 and 3,000, between 5 and 3,000, between 10 and 3,000, between 15 and 3,000, between 20 and 3,000, between 25 and 3,000, between 30 and 3,000, between 50 and 3,000, between 70 and 3,000, between 100 and 3,000, between 200 and 3,000, between 2 and 1,000, between 5 and 1,000, between 10 and 1,000, between 15 and 1,000, between 20 and 1,000, between 25 and 1,000, between 30 and 1,000, between 50 and 1,000, between 70 and 1,000, between 100 and 1,000, between 200 and 1,000, between 2 and 500, between 5 and 500, between 10 and 500, between 15 and 500, between 20 and 500, between 25 and 500, between 30 and 500, between 50 and 500, between 70 and 500, between 100 and 500, or between 200 and 500 nucleotide bases in length.

In some embodiments, a nucleic acid template may be single stranded or double-stranded. A single stranded nucleic acid template may also be referred to herein as a “polynucleotide template”. A nucleic acid template may be contained in a primary nucleic acid molecule. In some embodiments, a nucleic acid template may constitute the entirety of a primary nucleic acid molecule. In other embodiments, a nucleic acid template may be contained in a primary nucleic acid which contains one or more nucleotides which are not part of the nucleic acid template (e.g. the nucleic acid template may be of a shorter length than the primary nucleic acid which contains the nucleic acid template).

A nucleic acid template may be of any length of nucleotides. For example, a nucleic acid template may be at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 14, 16, 18, 20, 25, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length. In another example, a nucleic acid template may be between 2 and 100,000, between 5 and 100,000, between 10 and 100,000, between 15 and 100,000, between 20 and 100,000, between 25 and 100,000, between 30 and 100,000, between 50 and 100,000, between 70 and 100,000, between 100 and 100,000, between 200 and 100,000, between 2 and 10,000, between 5 and 10,000, between 10 and 10,000, between 15 and 10,000, between 20 and 10,000, between 25 and 10,000, between 30 and 10,000, between 50 and 10,000, between 70 and 10,000, between 100 and 10,000, between 200 and 10,000, between 2 and 5,000, between 5 and 5,000, between 10 and 5,000, between 15 and 5,000, between 20 and 5,000, between 25 and 5,000, between 30 and 5,000, between 50 and 5,000, between 70 and 5,000, between 100 and 5,000, between 200 and 5,000, between 2 and 3,000, between 5 and 3,000, between 10 and 3,000, between 15 and 3,000, between 20 and 3,000, between 25 and 3,000, between 30 and 3,000, between 50 and 3,000, between 70 and 3,000, between 100 and 3,000, between 200 and 3,000, between 2 and 1,000, between 5 and 1,000, between 10 and 1,000, between 15 and 1,000, between 20 and 1,000, between 25 and 1,000, between 30 and 1,000, between 50 and 1,000, between 70 and 1,000, between 100 and 1,000, between 200 and 1,000, between 2 and 500, between 5 and 500, between 10 and 500, between 15 and 500, between 20 and 500, between 25 and 500, between 30 and 500, between 50 and 500, between 70 and 500, between 100 and 500, or between 200 and 500 nucleotide bases in length.

A “primer” as used herein may refer to a polynucleotide which is i) capable of hybridizing to an original nucleic acid strand and ii) acting as a point of initiation for the synthesis of a new nucleic acid strand, wherein the new nucleic acid strand is an extension product of the primer and is complementary to the original strand. A primer may have a free —OH group at its 3′ terminus, which may serve as the origin of synthesis for the extension product.

A primer may contain standard nucleotides [e.g. standard DNA deoxyribonucleotides (deoxyadenosine monophosphate, deoxyguanosine monophosphate, thymidine monophosphate, deoxycytidine monophosphate) or standard RNA ribonucleotides (adenosine monophosphate, guanosine monophosphate, uridine monophosphate, cytidine monophosphate)], alternative nucleotides (e.g. inosine), modified nucleotides, nucleotide analogs, or a combination thereof. For example, an oligonucleotide primer may include peptide nucleic acids, morpholinos (e.g. phosphorodiamidate morpholino oligos), locked nucleic acids [see, for example, Kaur, H, et. al, Biochemistry 45 (23), 7347-55 (2006)], glycol nucleic acids, or threose nucleic acids. A primer may have a backbone, including, for example, phosphodiester linkages, phosphorothioate linkages (a non-bridging O is replaced with sulfur), or peptide linkages (as part of a peptide nucleic acid). Alternative nucleotides, modified nucleotides, and nucleotide analogs may be referred to collectively herein as “non-standard nucleotides.”

The presence of a non-standard nucleotide in a primer may affect various properties of the primer. In some embodiments, inclusion of a non-standard nucleotide in a primer may increase or decrease the thermodynamic stability of a primer to a complementary sequence thereof. For example, a primer having increased thermodynamic stability may contain a locked nucleic acid. A primer having decreased thermodynamic stability may contain, for example, inosine (described by Auer et al., Nucl. Acids Res. 24; 5021-5025 (1996)) or a negatively charged chemical group, such as a carboxylic acid.

A first primer or a second primer provided herein may be of any length. The first primer and second primer may contain the same number of nucleotides, or a different number of nucleotides. In some embodiments, a first or second primer may be at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length. In some embodiments, a first or second primer may be no more than 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length. In some embodiments, a first or second primer may have a length selected from a range having a minimum value of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, or 1000 nucleotides in length, and a maximum value of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length.

The tail region of a first primer or a second primer provided herein may be of any length. Typically, the tail regions of a first primer and a second primer directed to the same template contain the same number of nucleotides. In some embodiments, the tail region of a first or second primer may be at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length. In some embodiments, the tail region of a first or second primer may be no more than 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length. In some embodiments, the tail region of a first or second primer may have a length selected from a range having a minimum value of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, or 1000 nucleotides in length, and a maximum value of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length.

The template-binding region of a first primer or a second primer provided herein may be of any length. The template-binding regions of a first primer and a second primer directed to the same template may contain the same number of nucleotides, or a different number of nucleotides. In some embodiments, the template-binding region of a first or second primer may be at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length. In some embodiments, the template-binding region of a first or second primer may be no more than 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length. In some embodiments, the template-binding region of a first or second primer may have a length selected from a range having a minimum value of 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, or 1000 nucleotides in length, and a maximum value of 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 35, 40, 45, 50, 60, 70, 80, 90, 100, 150, 200, 250, 300, 350, 400, 500, 750, 1000, or 1500 nucleotides in length.

In some embodiments, a primer may be of any length and contain any nucleotide sequence which permits sufficiently stable and specific annealing of the primer to its complement at the temperature being used for a method or step thereof involving the primer. The exact length desired of a primer may depend on a variety of factors, including the temperature of a reaction, the chemical composition of the primer, and the reaction involving the primer. In some embodiments, the template-binding region of a primer may be of any length and contain any nucleotide sequence which permits sufficiently stable and specific annealing of the template-binding region of the primer to its complement at the temperature being used for a method or step thereof involving the primer. The exact length desired of the template-binding region of a primer may depend on a variety of factors, including the temperature of a reaction, the chemical composition of the template-binding region of the primer, and the reaction involving the primer. The inclusion of one or more non-standard nucleotides in the primer may change the desired length of the primer for use in a method provided herein, as compared to the length of a corresponding primer lacking a non-standard nucleotide. For example, if with a method provided herein it is desired to have a primer with a certain Tm, in some embodiments, a primer with the selected Tm may be of a shorter length if the primer contains at least some non-standard nucleotides, as compared to if the primer contains only standard nucleotides.

A primer provided herein may be prepared by any suitable method. For example, a primer may be chemically synthesized. In another example, a naturally occurring nucleic acid may be isolated, cleaved (e.g. with restriction enzymes), and/or modified to generate or to become part of a primer described herein.

In some embodiments, a label may be attached to a primer. Labels include, for example, binding ligands (e.g. digoxin or biotin), enzymes, fluorescent molecules/fluorophores, luminescent molecules, quencher molecules, or radioisotopes. In other embodiments, a base of an oligonucleotide may be replaced with a fluorescent analog, such as 2-aminopurine (see, for example, Proc. Acad. Sci. USA, 91, 6644-6648 (1994), which is herein incorporated by reference in its entirety).

In some embodiments, conditions such that: i) a template-binding region of a first copy of a first primer anneals to a strand of a nucleic acid template, ii) a template-binding region of a second primer anneals to an extension product of a first copy of a first primer, iii) a template-binding region of a second copy of a first primer anneals to an extension product of a second primer, or iv) a 3′ terminal region of an extension product of a second copy of a first primer of a first copy of a secondary nucleic acid anneals to a 3′ terminal region of an extension product of a second primer of a second copy of a secondary nucleic acid, to produce a cross-over structure comprising these strands, may each include incubating the nucleic acids at a temperature such that the strands of double-stranded nucleic acid molecules “breathe” (i.e. undergo brief periods of localized rupture of hydrogen bonds connecting base pairs) to a degree sufficient to facilitate the entry of a primer or different nucleic acid strand between the strands of a double-stranded molecule, and the annealing of the primer or different nucleic acid strand to one of the strands of the opened double-stranded nucleic acid molecule. In some embodiments, methods or steps thereof may be performed or incubated at a temperature of at least 10, 15, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 90, or 95 C. In some embodiments, methods or steps thereof may be performed or incubated at a temperature of no greater than 10, 15, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 90, or 95 C. In some embodiments, methods or steps thereof may be performed or incubated at a temperature between 10, 15, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, or 90 C and 15, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40, 41, 42, 43, 44, 45, 46, 47, 48, 49, 50, 51, 52, 53, 54, 55, 56, 57, 58, 59, 60, 61, 62, 63, 64, 65, 66, 67, 68, 69, 70, 71, 72, 73, 74, 75, 76, 77, 78, 79, 80, 81, 82, 83, 84, 85, 90 or 95 C.

In some embodiments, for a method or steps thereof provided herein, the step or method is performed at a temperature below the melting temperature (Tm) of the relevant potentially paired nucleotide strands, or regions thereof (e.g. the template-binding region of the first primer to the first strand of a nucleic acid template, the template-binding region of the second primer to the extension product of the first copy of the first primer, the first primer to the extension product of the second primer, the 3′ terminal region of the extension product of the second primer to its complement, the 3′ terminal region of the extension product of the first copy of the first primer to its complement, etc.). In some embodiments, for a method or steps thereof provided herein, the step or method is performed at a temperature above the Tm of the relevant potentially paired nucleotide strands, or regions thereof (e.g. the template-binding region of the first primer to the first strand of a nucleic acid template, the template-binding region of the second primer to the extension product of the first copy of the first primer, the first primer to the extension product of the second primer, the 3′ terminal region of the extension product of the second primer to its complement, the 3′ terminal region of the extension product of the first copy of the first primer to its complement, etc.). Generally, melting temperature is regarding as the temperature at which 50% of nucleic acids having a given mutually complementary nucleotide sequence are base-paired.

In some embodiments, a nucleic acid polymerase is included with a method or composition provided herein. A polymerase may generate an extension product of a primer. The primer and extension product thereof may be complementary to a template nucleic acid strand. Generally, a nucleic acid polymerase will initiate synthesis of an extension product of a primer at the 3′ end of the primer. In some embodiments, a DNA polymerase is included with a method or composition provided herein. As used herein, a “DNA polymerase” refers to a nucleic acid polymerase which has primary or exclusive polymerase activity on DNA templates. In some embodiments, a reverse transcriptase is included with a method or composition provided herein. As used herein, a “reverse transcriptase” refers to a nucleic acid polymerase which can synthesize a DNA strand from an RNA template.

In some embodiments, a polymerase provided herein may have strand displacement activity. Polymerases having strand displacement activity include, for example, exo-Bca DNA polymerase, phi29 DNA polymerase, Klenow Fragment of E. coli DNA Polymerase I, Vent_(R) DNA polymerase, Deep Vent_(R) DNA polymerase, 9° N_(m) DNA polymerase, and Large Fragment of Bst DNA Polymerase.

Modified versions of polymerases may also be used with the methods and compositions provided herein, provided that the modified polymerase has sequence-dependent nucleic acid synthesis activity. A modified version of a polymerase (“modified polymerase”) may have, for example, 100 or fewer, 70 or fewer, 50 or fewer, 40 or fewer, 30 or fewer, 20 or fewer, 10 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, 2 or fewer, or 1 different amino acid from the sequence of the parent version of the polymerase. In some embodiments, a modified polymerase may contain no more than 1000, 700, 500, 400, 300, 200, 100, 50, 40, 30, 20, 10, or 5 greater or fewer amino acids than the parent polymerase. In some embodiments, a modified polymerase may comprise a fragment of a parent polymerase. In some embodiments, a modified polymerase may comprise a chimeric polypeptide with a portion derived from a polymerase and a portion derived from a non-polymerase protein. In some embodiments, a modified polymerase may have, for example, increased catalytic activity, increased stability, or increased thermostability as compared to the parent polymerase.

In some embodiments, a polymerase provided herein is thermostable. A thermostable polymerase may have, for example, a half-life of at least 5, 10, 15, 20, 30, 40, 50, 60, 90, 120, or 180 minutes at a temperature of at up to 25, 30, 35 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 C. In some embodiments, a modified polymerase may be thermostable.

In some embodiments, methods and steps thereof provided herein include or are performed under conditions sufficient to support polymerase-based nucleic acid synthesis. Example conditions for polymerase-based nucleic acid synthesis are known in the art and are provided, for example, in Green and Sambrook, supra. Non-limiting components for a polymerase-based nucleic acid synthesis reaction may include one or more of: polymerase enzyme (at a concentration between, for example, 0.01 and 10 units enzyme per 50 microliters reaction volume, or any range therein including, for example, between 0.01-1, 0.1-10, 0.1-5, 0.5-10, 0.5-5, 0.5-2, 1-10, or 1-5 units enzyme per 50 microliters reaction volume, where 1 unit of enzyme will incorporate 15 nmol of dNTPs into polymerization product in 30 minutes at 75 C); template (at a concentration of at least, for example, 1, 10, 100, 1,000, 10,000, or 100,000 copies per reaction); primer (at a concentration between, for example, 0.01 and 10 micromolar, or any range therein including, for example, between 0.01-1, 0.1-10, 0.1-5, 0.5-5, or 0.5-2 micromolar); dNTPs (e.g. dATP, dTTP, dGTP, and dCTP, at a concentration between, for example, 50 and 500 micromolar each of dATP, dTTP, dGTP, and dCTP, or any range therein including, for example, between 50-350, 100-500, 100-300, 200-500, or 300-400 micromolar each of dATP, dTTP, dGTP, and dCTP); salt (e.g. KCl or potassium acetate, at a concentration between, for example, 1 and 200 millimolar, or any range therein including, for example, between 1-100, 1-50, 1-20, 1-10, 10-20, 10-50, or 10-200 millimolar); buffer (e.g. Tris-HCl or Tris-acetate, pH 7.8-8.5, at a concentration between, for example, 1 and 100 millimolar, or any range therein including, for example, between 1-50, 1-20, 1-10, 1-5, 10-100, 20-100, or 50-100 millimolar); and magnesium ions (at a concentration between, for example 0.1 and 10 millimolar, or any range therein, including, for example, between 0.1-5, 0.1-1, 0.5-10, 0.5-5, or 0.5-2.5 millimolar). Additional non-limiting components for a polymerase-based nucleic acid synthesis reaction may increase the speed of the reaction, increase the fidelity of the reaction, or increase the stability of enzymes or DNA in the reaction, and may include one or more of: gelatin (at a concentration between, for example, 0.0001% and 0.1% w/v), BSA (at a concentration between, for example, 0.01 and 1 microgram per microliter), sucrose (at a concentration between, for example 0.01 molar and 0.8 molar), trehalose (at a concentration between, for example 0.01 molar and 0.8 molar), DMSO (at a concentration between, for example, 0.01 and 10% v/v), betaine (at a concentration between, for example, 0.1 and 10 molar), formamide (at a concentration between, for example, 0.1 and 10% v/v), glycerol (at a concentration between, for example, 0.1 and 20% v/v), polyethylene glycol (at a concentration between, for example, 0.1 and 20% v/v), non-ionic detergents [e.g. NP-40 (at a concentration between, for example, 0.01 and 1% v/v), Tween-20 (at a concentration between, for example, 0.01 and 1% v/v), and Triton X-100 (at a concentration between, for example, 0.01 and 1% v/v)], ammonium ions [e.g. ammonium sulfate (at a concentration between, for example, 1 and 100 millimolar)], and EDTA (at a concentration between, for example, 0.001 and 0.1 millimolar). Other reagents may also be present in a polymerase-based nucleic acid synthesis reaction provided herein. For example, reagents to sufficient to synthesize RNA reaction products or reaction products containing non-standard nucleotides may be used. Conditions sufficient to support polymerase-based nucleic acid synthesis may include a variety of temperatures and pH values. For example, the pH of a of a polymerase-based nucleic acid synthesis reaction be between, for example pH 6.0 and pH 10.0, such as 6.5, 7, 7.5, 7.8, 7.9, 8, 8.1, 8.2, 8.5, 9, or 9.5. The temperature of a polymerase-based nucleic acid synthesis reaction may be constant or varied. A constant temperature may be between, for example, 10 C and 95 C, such as 20, 25, 30, 35, 37, 40, 42, 45, 50, 55, 60, 65, 70, 75, 80, or 85 C. A varied temperature may at two or more different temperatures between, for example 10C and 95 C, such two or more temperatures selected from 20, 25, 30, 35, 37, 40, 42, 45, 50, 55, 60, 65, 70, 75, 80, or 85 C.

Methods provided herein may be performed at a variety of temperatures. In some embodiments, all steps of a method are performed at the same temperature. Thus, temperature cycling such as in PCR is not necessary with methods disclosed herein. In some embodiments, methods provided herein may be performed at two or more different temperatures. In some embodiments, a reaction mixture containing reagents for a method provided herein is incubated at two or more different temperatures. In some examples, different temperatures may be selected to optimize the rate, accuracy, or other feature of different steps of a method provided herein. For example, a temperature may be selected to increase the enzymatic activity of a polymerase. In some examples, different temperatures may be selected to increase the binding specificity of a primer to a template or to increase the accessibility of a template to a primer (e.g. higher temperatures may promote the separation of duplex template nucleic acids). In some embodiments, all of the steps of a method provided herein are performed at a temperature of no greater than 80, 70, 60, 50, 40, 30, 20 or 10° C. In some embodiments, a method provided herein is performed at a temperature between 20-60, 30-70, 40-80, 30-40, 35-45, 40-50, 45-55, 50-60, or 55-65° C. Methods disclosed herein may be performed with or without a thermocycler.

As one consideration, the temperature used for a method or step thereof provided herein may be selected to be appropriate for the enzyme(s) being used in the step of the method. In some embodiments, for methods in which a polymerase is used, the temperature(s) of the reaction is selected such that it does not significantly impair the activity of the polymerase (e.g. the temperature of the reaction may be selected such that polymerase has a half-life of at least 24, 12, 6, 4, 3, 2, 1, 0.75, 0.5, 0.25, or 0.1 hours). Alternatively, methods may be performed at a temperature that impairs the activity of the enzyme(s) being used in the method (e.g. the temperature of the reaction may be selected such that an enzyme in the reaction has a half-life of no more than 24, 12, 6, 4, 3, 2, 1, 0.75, 0.5, 0.25, or 0.1 hours). In some embodiments, if a method is performed at a temperature or other condition (e.g. pH) that impairs the activity of one or more the enzymes, additional enzyme may be added to the reaction at one or more intervals after the initiation of the method to supplement the activity of the impaired enzyme(s).

In some embodiments, one or more steps of a method provided herein occur in the same reaction vessel (e.g. tube, tip, container, etc.). In some embodiments, all of the steps of a method occur in the same reaction vessel.

Reagents for methods provided herein can all be provided together at the start of a reaction, or they may be added sequentially, where after one, two, or more steps new reagents are added to a reaction. In some circumstances, new reagents (e.g. enzymes, primers) may be added to a reaction vessel during the course of the reaction, to increase the amount of reagents available to act on substrates or to replace the function of reagents that have become inactivated (e.g. enzymes). New reagents may be added to a reaction at one or more selected time intervals after the initiation of a reaction of a method provided herein (for example, at 1, 3, 5, 7, 10, 15, 20, 30, 45, or 60 minutes after the initiation of a reaction).

In some embodiments, one or more steps of a method provided herein may occur simultaneously. For example, after the generation of a single copy of an extension product of a first copy of the first primer, multiple copies of an extension product of a second primer may be sequentially generated from that single copy of an extension product of a first copy of the first primer. As copies of the extension product of a second primer are sequentially generated from the single copy of the extension product of a first copy of the first primer, the individual copies of the extension product of a second primer may, for example, serve as a template for the formation of an extension product of a second copy of the first primer, be a component of a secondary nucleic acid, be a component of a cross-over structure, or may be an initiation point for the formation of an extension product of an extension product of a second primer/first concatemer strand. In another example, two copies of a secondary nucleic acid may form a cross-over structure at the same time that an extension product of a first copy of a first primer is generated from a first strand of a nucleic acid template. In another example, one copy of an extension product of a first copy of a first primer is generated from a first strand of a nucleic acid template at the same time that an extension product of the second primer is generated from a different copy of the extension product of a first copy of a first primer. In addition, in methods and compositions provided herein involving a double-stranded nucleic acid template, either strand of the nucleic acid template may be considered a “first strand”, and either primer of a primer pair provided herein may be considered a “first primer”. Accordingly, in some examples, both strands of a double-stranded nucleic acid may be simultaneously used as “first strand” of a nucleic acid according to a method provided herein, with opposite primers of the primer pair serving as the “first primer” for the different “first strands”.

Reactions and compositions provided herein may contain multiple copies of first primers, second primers, primary nucleic acids, secondary nucleic acids, extension products of a first copy of the first primer, extension products of a second copy of the first primer, extension products of the second primer, cross-over structures, concatemers, and the like. Accordingly, methods provided herein may include processes wherein multiple steps provided herein occur simultaneously, and such steps may occur with multiple copies of the relevant molecules.

In some embodiments, two or more sets of first and second primers are provided in a method provided herein, where each set contains a first primer and a second primer, and where different primer sets are complementary to different linear nucleic acid templates. The template-binding region of both the first and second primers in a set may be complementary to different strands of the same nucleic acid template. Typically, the tail regions of the first and second primers in a given set have different, non-complementary sequences from the tail regions of the first and second primer of other primer sets to be used in the same method or composition, so that the primer tails from the different primer sets are not complementary. This may be desirable in order to prevent the formation of hybrid cross-over structures containing strands derived from different nucleic acid templates. Alternatively, tail regions of the first and second primers in two or more different primer sets may have complementary sequences, in order to create hybrid cross-over structures and concatemers containing strands derived from different nucleic acid templates. Inclusion of two or more primer sets in a method provided herein may support the simultaneous amplification of multiple different nucleic acid templates in the same reaction vessel. This may be useful, for example, for amplifying multiple templates of interest in a sample, or for assaying for the presence of multiple different templates in a sample. In some embodiments, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 40, 50, 60, 70, 100, 200, 500 or more sets of first and second primers are provided in a method provided herein, in order to amplify or assay for the presence of 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 25, 30, 40, 50, 60, 70, 100, 200, 500 or more different nucleic acid templates.

In some embodiments, in a method provided herein, a nucleic acid template may be amplified rapidly. For example, in some embodiments, a nucleic acid template may be amplified at least 500-fold within 0.1, 0.5, 1, 3, 5, 10, 15, 20, 30, 40, 50, 60, 90, 120, or 180 minutes of starting the method. In another example, in some embodiments, a nucleic acid template may be amplified at least 10,000-fold within 0.1, 0.5, 1, 3, 5, 10, 15, 20, 30, 40, 50, 60, 90, 120, or 180 minutes of starting the method. In another example, in some embodiments, a nucleic acid template may be amplified at least 5, 10, 25, 50, 100, 250, 500, 1,000, 5,000, 10,000, 50,000, 100,000, 500,000, or 1,000,000-fold over the original amount of the nucleic acid template present in a reaction mixture at the start of the method within 0.1 minute, 0.5 minute, 1 minute, 3 minutes, 5 minutes, 10 minutes, 15 minutes, 20 minutes, 30 minutes, 40 minutes, 50 minutes, 60 minutes, 90 minutes, 2 hours, 3 hours, 4 hours, 6 hours, 8 hours, 12 hours, 16 hours, or 24 hours of initiation of the method. In some embodiments, when a method is initiated, all of the reagents for the first step of the method are in a vessel containing the reaction mixture for the method. In some embodiments, when a method is initiated, all of the reagents for all of the steps of the method are in a vessel containing the reaction mixture for the method.

In some embodiments, in a method provided herein, a nucleic acid template may be amplified at greater than a linear rate. In some embodiments, in a method provided herein, a nucleic acid template may be amplified exponentially. In some embodiments, in a method provided herein, a nucleic acid template may at least double in number every 1, 2, 3, 5, 10, 15, 20, 25, 30, 45, 60, 90, 120, 180, or 240 minutes after the initiation of the method. In some embodiments, a nucleic acid template may amplified at least 5, 10, 25, 50, 100, 250, 500, 1,000, 5,000, 10,000, 50,000, 100,000, 500,000, 1,000,000, or 10,000,000-fold over the original amount of the nucleic acid template present in the reaction at the start of the method.

The presence of multiple copies of a nucleic acid template in a concatemer generated according to a method provided herein may contribute to the rapid amplification of nucleic acid templates according to methods provided herein. In particular, since multiple copies of a strand of a nucleic acid template may be present in a single concatemer strand, the loading of a single polymerase onto a single concatemer strand may result in the generation of multiple copies of a strand of the nucleic acid template. In some situations, the time required for nucleic acid polymerases to encounter and load onto nucleic acid strands may significantly impact the overall speed of an amplification reaction. For example, if each nucleic acid strand that a polymerase encounters during a replication reaction only contains a single copy of a strand of a nucleic acid template, a polymerase may need to encounter and load onto a new template strand after each copy of the strand of the template is generated. In contrast, with a concatemer, after the polymerase encounters and loads on a concatemer strand, it may synthesize multiple copies of a strand of the template without needing to leave the concatemer strand or encounter and load onto another strand.

In some embodiments, provided herein are methods and compositions for the generation of a double-stranded DNA concatemer from a single-stranded RNA template. The method may be performed as described herein, except that a reverse transcriptase enzyme (e.g. AMV reverse transcriptase, M-MLV reverse transcriptase, Superscript II™ reverse transcriptase, Superscript III™ reverse transcriptase, or ThermoScript™ reverse transcriptase) is also included with the methods provided herein. The first copy of the first primer may anneal to the RNA template, and the reverse transcriptase enzyme may generate the extension product of the first copy of the first primer. Methods and conditions for reverse transcription of RNA are known in the art and are disclosed, for example, in RNA: A Laboratory Manual, D. Rio et al., Cold Spring Harbor Laboratory Press (2011), which is herein incorporated by reference in its entirety. After the generation of the extension product of the first copy of the first primer by a reverse transcriptase enzyme, the rest of the steps for the generation of a concatemer may be the same as described elsewhere herein.

In some embodiments, methods and compositions provided herein may include one or more “bumping primers”. Bumping primers may be used with methods and compositions provided herein to, for example, increase the rate or specificity of generation of reaction products by increasing the rate at which first primer extension products are displaced from a primary nucleic acid As used herein a “bumping primer” refers to a primer which is complementary to a sequence on a first strand or second strand of a nucleic acid template which is downstream from a sequence on the same strand to which the template-binding region of a first primer or second primer binds. Thus, when a bumping primer is annealed to the same nucleic acid strand that a first primer or second primer is annealed to, the 3′ terminus of the bumping primer is oriented towards the 5′ terminus of the first primer or second primer (i.e. the 5′ terminal nucleotide and tail region of the first primer or second primer). When incubated with a nucleic acid polymerase and under conditions to support the generation of primer extension products, an extension product of a bumping primer may be formed by the polymerase, from the 3′ terminus of the bumping primer. Since the 3′ terminus of the bumping primer is oriented toward the 5′ terminus of the first primer or second primer, as the extension product of the bumping primer increases in length, it may eventually encounter the 5′ terminus of the first primer or second primer as the extension product. The polymerase may then displace the first primer or second primer from the strand, as well as any extension product of the first primer or second primer. Accordingly, bumping primers may accelerate reactions provided herein.

In some embodiments, provided herein is a vessel containing one or more enzymes, primers, or other reagents provided herein. Vessels may include any structure capable of supporting or containing a liquid or solid material and may include, tubes, containers, tips, etc. In some embodiments, a wall of a vessel may permit the transmission of light through the wall. A vessel may be optically clear. A vessel may contain, for example, any one or more of an isolated nucleic acid polymerase, an isolated DNA polymerase, an isolated reverse transcriptase, a first primer, a second primer, a nucleic acid dye, or a nucleic acid probe, as described elsewhere herein. Any number of copies of any of the contents of a vessel may be provided (e.g. a first copy, a second copy, a third copy, etc.) The contents of a vessel may be in fluid communication. In some embodiments, a vessel may further contain a nucleic acid template. In some embodiments, a vessel may further contain nucleotides, buffers, salts, water, or other reagents provided herein for the amplification of nucleic acids. In some embodiments, a vessel may contain two or more sets of primers, wherein each primer set comprises a first and second primer, and the different primer sets are complementary to different nucleic acid templates.

Two or more reagents useful for a method provided herein may be packaged and provided as a kit. For example, a kit may include any two or more of: a nucleic acid template, a first primer, a second primer, a nucleic acid polymerase, a DNA polymerase, a reverse transcriptase, buffers, a nucleic acid dyes, a nucleic acid probe, or dNTPs, as described elsewhere herein. Within the kit, the two or more reagents may be packaged in separate vessels or the same vessel. In some embodiments, a kit may further contain nucleotides, buffers, salts, water, or other reagents provided herein for the amplification of nucleic acids.

In some embodiments, a nucleic acid ligase may be included with a method or composition provided herein. Ligases catalyze the formation of phosphodiester bonds between nucleotides, typically between the 5′ phosphate of one nucleotide, and the 3′ hydroxyl group of another nucleotide. A reaction provided herein may amplify a target nucleic acid at a greater rate with the inclusion of a ligase in the reaction, as compared to the reaction without the inclusion of a ligase. A ligase may, for example, increase the size or number of concatemers present in a reaction provided herein.

Nucleic acid ligases include E. coli DNA ligase, Taq DNA ligase, T3 DNA ligase, T4 DNA ligase, T7 DNA ligase, Ampligase™, T4 RNA ligase 1, and T4 RNA ligase 2.

In order to catalyze the ligation reaction, certain ligases require ATP (e.g. T4 DNA ligase) or NAD+ (E. coli DNA ligase). In some embodiments, a ligase may ligate nucleic acids having blunt ends. In some embodiments, a ligase may ligate nucleic acids having sticky ends. In some embodiments, a ligase may ligate nucleic acids having both blunt and sticky ends.

Modified versions ligases may also be used with the methods and compositions provided herein, provided that the modified ligase has the ability to catalyze the formation of phosphodiester bonds between nucleotides. A modified version of a ligase (“modified ligase”) may have, for example, 100 or fewer, 70 or fewer, 50 or fewer, 40 or fewer, 30 or fewer, 20 or fewer, 10 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, 2 or fewer, or 1 different amino acid from the sequence of the parent, naturally occurring version of the ligase. In some embodiments, a modified ligase may contain no more than 1000, 700, 500, 400, 300, 200, 100, 50, 40, 30, 20, 10, or 5 greater or fewer amino acids than the parent ligase. In some embodiments, a modified ligase may comprise a fragment of a parent ligase. In some embodiments, a modified ligase may comprise a chimeric polypeptide with a portion derived from a ligase and a portion derived from a non-ligase protein. In some embodiments, a modified ligase may have, for example, increased catalytic activity, increased stability, or increased thermostability as compared to the parent ligase.

In some embodiments, a ligase provided herein is thermostable. A thermostable ligase may have, for example, a half-life of at least 5, 10, 15, 20, 30, 40, 50, 60, 90, 120, or 180 minutes at a temperature of at up to 25, 30, 35 40, 45, 50, 55, 60, 65, 70, 75, 80, 85, 90, or 95 C. In some embodiments, a modified ligase may be thermostable.

In some embodiments, a ligase included with methods and compositions provided herein may be a modified ligase referred to herein as “p50-Tth”, which has the amino acid sequence: mghhhhhhhhhhssghiegrasadgpylqileqpkqrgfrfryvcegpshgglpgasseknkksypqvkicnyvgpakvivqlvtng knihlhahslvgkhcedgictvtagpkdmvvgfanlgilhvtkkkvfetlearmteacirgynpgllvhpdlaylqaegggdrqlgdrek elirqaalqqtkemdlsvvrlmftaflpdstgsfirrlepvvsdaiydskapnasnlkivrmdrtagcvtggeeiyllcdkvqkddiqirfye eeenggvwegfgdfsptdvhrqfaivflapkykdinitkpasvfvqlrrksdletsepkpflyypeikdkeevqrkrqkgssgtsgggsgg gmtleearkrvnelrdliryhnyryyvladpeisdaeydrllrelkeleerfpelkspdsptlqvgarpleatfrpvrhptrmysldnafnld elkafeerieralgrkgpfaytvehkvdglsvnlyyeegylvygatrgdgevgeevtqnlltiptiprrlkgvperlevrgevympieaflr lneeleergerifknprnaaagslrqkdpritakrglratfyalglgleeveregvatqfallhwlkekgfpvehgyaravgaegveavyq dwlkkrralpfeadgvvvkldelalwrelgytaraprfaiaykfpaeeketrlldvvfqvgrtgrvtpvgilepvflegsevsrvtlhnesy ieeldirigdwvlvhkaggvipevlrylkerrtgeerpirwpetcpecghrllkegkvhrcpnplcpakrfeairhfasrkamdiqglge klierllekglvkdvadlyrlrkedlvglermgeksaqnllrqieeskkrglerllyalglpgvgevlarnlaarfgnmdrlleasleelleve evgeltarailetlkdpafrdlvalkeagvemeakekggealkgltfvitgelsrpreevkallalgakvtdsysrktsylvvgenpgskl ekaralgvptlteeelyrlleartgkkaeelv. Ligase p50-Tth has thermostable blunt-end ligation activity at temperatures of at least 60 C. Ligase p50-Tth is a chimeric protein which comprises a His 10-containing leader sequence, a p50 sequence from the human NF-kappa-B protein accession number NP_003989 amino acids 40-366 (indicated in italics), a flexible glycine rich sequence, and a Tth DNA ligase, from Thermus Thermophilus HB8, accession YP_144363 (indicated with underlining). In some embodiments, a modified version of p50-Tth ligase may be used with methods and compositions provided herein (e.g. with 100 or fewer, 70 or fewer, 50 or fewer, 40 or fewer, 30 or fewer, 20 or fewer, 10 or fewer, 5 or fewer, 4 or fewer, 3 or fewer, 2 or fewer, or 1 different amino acids from p50-Tth ligase).

Applications

The various methods and compositions provided herein for the amplification of a nucleic acid template/the generation of a concatemer containing at least two copies of the template can fulfill many of the functions that have previously been carried out by other methods and compositions for isothermal and thermocycler-dependent nucleic acid amplification. A nucleic acid template for amplification according to methods provided herein may also be referred to herein as a “target nucleic acid”. Methods and compositions provided herein may be used, for example, for isolation and cloning of nucleic acids of interest, gene expression analysis, diagnostic identification of nucleic acids, synthesis of novel nucleic acids, nucleic acid probe synthesis and labeling, forensic identification of a subject, allele identification from a subject, genetic screening, nucleic acid sequencing, and related applications. A target nucleic acid molecule may be of any type, including single-stranded or double stranded and DNA or RNA (e.g. mRNA). A target nucleic acid may be of any type or function (e.g. a protein-coding sequence, a regulatory sequence, an intron, etc.). A target nucleic acid may be the entirety of a gene, or a portion thereof.

In some embodiments, a method or composition provided herein may be used to detect the amount of a target nucleic acid in a sample (including the presence or absence of the target), to measure the amount of an amplification product of a target formed from a sample in a selected period of time, or to determine the amount of time necessary to generate a certain number of copies of a template from a sample. Samples which may be used with methods and compositions provided herein are described elsewhere herein, and may include, for example, a bodily fluid, a secretion, or a tissue of a subject.

In some embodiments, a method provided herein may be performed to simultaneously assay for at least 2, 3, 4, 5, 6, 7, 8, 9, 10, 12, 15, 20, 25, 30, 35, 40, 45, 50, 75, 100, or more different target nucleic acids in the same reaction vessel. Typically, for each target nucleic acid of interest, a first primer and a second primer are provided, each being complementary to a strand of the nucleic acid target, or a complement thereof. The amplification of the different target nucleic acids in the same vessel may be monitored, for example, by the use of nucleic acid probes having sequence specificity for detection sequences in the different target nucleic acids, and different fluorophores.

In some embodiments, a method or composition provided herein may be used to detect the presence or absence of a particular nucleotide of interest in a target nucleic acid (e.g. in the case of a mutation or SNP). For example, a first or second primer may be selected which selectively binds to a region in a target nucleic acid which includes or is adjacent to the nucleotide of interest. The primer may be designed such that it selectively either: i) binds to the region when the region contains the nucleotide of interest, or ii) does not bind to the region when the region contains the nucleotide of interest. A method as described herein may be performed with the selected primer, and the outcome of the amplification reaction may provide information regarding the presence or absence of the nucleotide of interest in the target nucleic acid. For example, if the template-binding region of a first primer is designed to have a nucleotide sequence which is complementary to a sequence in the target nucleic acid which includes a particular nucleotide of interest (e.g. a mutation), successful amplification of the target nucleic acid with the selected primer from a sample may indicate that the sample contains a target nucleic acid having the particular nucleotide of interest. In some embodiments, a primer used for analysis of a nucleotide of interest in a target nucleic acid may contain a critical nucleotide at the 3′ terminus of the primer. In such a case, the annealing of the 3′ terminal nucleotide of the primer may be dependent on the presence of the nucleotide of interest in the target nucleic acid. If the 3′ terminal nucleotide of the primer does not anneal with a nucleotide in the target nucleic acid (e.g. due to a mismatch between the nucleotides), the mismatch may significantly impair a nucleic acid polymerase from synthesizing an extension product from the primer. Accordingly, in some embodiments, a primer having a 3′ terminal nucleotide which corresponds to a nucleotide of interest may be useful for determining the presence or absence of a particular nucleotide in a target nucleic acid.

Methods and compositions provided herein may be used to amplify a nucleic acid from any sample which may contain nucleic acids. Examples of samples may include various fluid samples. In some instances, the sample may be a bodily fluid sample from a subject. The sample may include one or more fluid component. In some instances, solid or semi-solid samples may be provided. The sample may include tissue collected from the subject. The sample may include a bodily fluid, secretion, or tissue of a subject. The sample may be a biological sample. The biological sample may be a bodily fluid, a secretion, or a tissue sample. Examples of biological samples may include but are not limited to, blood, serum, saliva, urine, gastric and digestive fluid, tears, stool, semen, vaginal fluid, interstitial fluids derived from tumorous tissue, ocular fluids, sweat, mucus, earwax, oil, glandular secretions, breath, spinal fluid, hair, fingernails, skin cells, plasma, nasal swab or nasopharyngeal wash, spinal fluid, cerebral spinal fluid, tissue, throat swab, biopsy, placental fluid, amniotic fluid, cord blood, emphatic fluids, cavity fluids, sputum, pus, microbiota, meconium, breast milk or other excretions. The sample may be provided from a human or animal. Samples may be from a plant, microorganism (e.g. virus, bacteria), or other biological material.

In some embodiments, methods and compositions provided herein may be performed at or used at point of service locations (e.g. a subject's home or work, grocery stores, drug stores, clinics, schools, etc.). Methods and compositions provided herein may permit the rapid amplification of nucleic acids in a sample from a subject, in order to aid in the diagnosis or treatment of a subject.

The assays and methods disclosed herein may be performed on a device, or on a system, for processing a sample. The assays and methods disclosed herein can be readily incorporated into and used in device for processing a sample, or a system for processing a sample, which may be an automated assay device, or may be an automated assay system. Such a device, and such a system, may be useful for the practice of the methods disclosed herein. For example, a device may be useful for receiving a sample. A device may be useful for preparing, or for processing a sample. A device may be useful for performing an assay on a sample. A device may be useful for obtaining data from a sample. A device may be useful for transmitting data obtained from a sample. A device may be useful for disposing of a sample following processing or assaying of a sample.

A device may be part of a system, a component of which may be a sample processing device. A device may be a sample processing device. A sample processing device may be configured to facilitate collection of a sample, prepare a sample for a clinical test, or perform a method with one or more reagents, as disclosed herein. A sample processing device may be configured to obtain data from a sample. A sample processing device may be configured to transmit data obtained from a sample. A sample processing device may be configured to analyze data from a sample. A sample processing device may be configured to communicate with another device, or a laboratory, or an individual affiliated with a laboratory, to analyze data obtained from a sample.

A sample processing device may be configured to be placed in or on a subject. A sample processing device may be configured to accept a sample from a subject, either directly or indirectly. A sample may be, for example, a blood sample (e.g., a sample obtained from a fingerstick, or from venipuncture, or an arterial blood sample), a urine sample, a biopsy sample, a tissue slice, stool sample, or other biological sample; a water sample, a soil sample, a food sample, an air sample; or other sample. A blood sample may comprise, e.g., whole blood, plasma, or serum. A sample processing device may receive a sample from the subject through a housing of the device. The sample collection may occur at a sample collection site, or elsewhere. The sample may be provided to the device at a sample collection site.

In some embodiments, a sample processing device may be configured to accept or hold a cartridge. In some embodiments, a sample processing device may comprise a cartridge. The cartridge may be removable from the sample processing device. In some embodiments, a sample may be provided to the cartridge of the sample processing device. Alternatively, a sample may be provided to another portion of a sample processing device. The cartridge and/or device may comprise a sample collection unit that may be configured to accept a sample.

A cartridge may include a sample, and may include reagents for use in processing or testing a sample, disposables for use in processing or testing a sample, or other materials. A cartridge may contain reagents disclosed herein for the performing a method disclosed herein. Following placement of a cartridge on, or insertion of a cartridge into, a sample processing device, one or more components of the cartridge may be brought into fluid communication with other components of the sample processing device. For example, if a sample is collected at a cartridge, the sample may be transferred to other portions of the sample processing device. Similarly, if one or more reagents are provided on a cartridge, the reagents may be transferred to other portions of the sample processing device, or other components of the sample processing device may be brought to the reagents. In some embodiments, the reagents or components of a cartridge may remain on-board the cartridge. In some embodiments, no fluidics are included that require tubing or that require maintenance (e.g., manual or automated maintenance).

A sample or reagent may be transferred to a device, such as a sample processing device. A sample or reagent may be transferred within a device. Such transfer of sample or reagent may be accomplished without providing a continuous fluid pathway from cartridge to device. Such transfer of sample or reagent may be accomplished without providing a continuous fluid pathway within a device. In embodiments, such transfer of sample or reagent may be accomplished by a sample handling system (e.g., a pipette); for example, a sample, reagent, or aliquot thereof may be aspirated into an open-tipped transfer component, such as a pipette tip, which may be operably connected to a sample handling system which transfers the tip, with the sample, reagent, or aliquot thereof contained within the tip, to a location on or within the sample processing device. The sample, reagent, or aliquot thereof can be deposited at a location on or within the sample processing device. Sample and reagent, or multiple reagents, may be mixed using a sample handling system in a similar manner. One or more components of the cartridge may be transferred in an automated fashion to other portions of the sample processing device, and vice versa.

A device, such as a sample processing device, may have a fluid handling system. A fluid handling system may perform, or may aid in performing, transport, dilution, extraction, aliquotting, mixing, and other actions with a fluid, such as a sample. In some embodiments, a fluid handling system may be contained within a device housing. A fluid handling system may permit the collection, delivery, processing and/or transport of a fluid, dissolution of dry reagents, mixing of liquid and/or dry reagents with a liquid, as well as collection, delivery, processing and/or transport of non-fluidic components, samples, or materials. The fluid may be a sample, a reagent, diluent, wash, dye, or any other fluid that may be used by the device, and may include, but not limited to, homogenous fluids, different liquids, emulsions, suspensions, and other fluids. A fluid handling system, including without limitation a pipette, may also be used to transport vessels (with or without fluid contained therein) around the device. The fluid handling system may dispense or aspirate a fluid. The sample may include one or more particulate or solid matter floating within a fluid.

In embodiments, a fluid handling system may comprise a pipette, pipette tip, syringe, capillary, or other component. The fluid handling system may have portion with an interior surface and an exterior surface and an open end. The fluid handling system may comprise a pipette, which may include a pipette body and a pipette nozzle, and may comprise a pipette tip. A pipette tip may or may not be removable from a pipette nozzle. In embodiments, a fluid handling system may use a pipette mated with a pipette tip; a pipette tip may be disposable. A tip may form a fluid-tight seal when mated with a pipette. A pipette tip may be used once, twice, or more times. In embodiments, a fluid handling system may use a pipette or similar device, with or without a pipette tip, to aspirate, dispense, mix, transport, or otherwise handle the fluid. The fluid may be dispensed from the fluid handling system when desired. The fluid may be contained within a pipette tip prior to being dispensed, e.g., from an orifice in the pipette tip. In embodiments, or instances during use, all of the fluid may be dispensed; in other embodiments, or instances during use, a portion of the fluid within a tip may be dispensed. A pipette may selectively aspirate a fluid. The pipette may aspirate a selected amount of fluid. The pipette may be capable of actuating stirring mechanisms to mix the fluid within the tip or within a vessel. The pipette may incorporate tips or vessels creating continuous flow loops for mixing, including of materials or reagents that are in non-liquid form. A pipette tip may also facilitate mixture by metered delivery of multiple fluids simultaneously or in sequence, such as in 2-part substrate reactions.

The fluid handling system may include one or more fluidically isolated or hydraulically independent units. For example, the fluid handling system may include one, two, or more pipette tips. The pipette tips may be configured to accept and confine a fluid. The tips may be fluidically isolated from or hydraulically independent of one another. The fluid contained within each tip may be fluidically isolated or hydraulically independent from one fluids in other tips and from other fluids within the device. The fluidically isolated or hydraulically independent units may be movable relative to other portions of the device and/or one another. The fluidically isolated or hydraulically independent units may be individually movable. A fluid handling system may comprise one or more base or support. A base or support may support one or more pipette or pipette units. A base or support may connect one or more pipettes of the fluid handling system to one another.

A sample processing device may be configured to perform processing steps or actions on a sample obtained from a subject. Sample processing may include sample preparation, including, e.g., sample dilution, division of a sample into aliquots, extraction, contact with a reagent, filtration, separation, centrifugation, or other preparatory or processing action or step. A sample processing device may be configured to perform one or more sample preparation action or step on the sample. Optionally, a sample may be prepared for a chemical reaction and/or physical processing step. A sample preparation action or step may include one or more of the following: centrifugation, separation, filtration, dilution, enriching, purification, precipitation, incubation, pipetting, transport, chromatography, cell lysis, cytometry, pulverization, grinding, activation, ultrasonication, micro column processing, processing with magnetic beads, processing with nanoparticles, or other sample preparation action or steps. For example, sample preparation may include one or more step to separate blood into serum and/or particulate fractions, or to separate any other sample into various components. Sample preparation may include one or more step to dilute and/or concentrate a sample, such as a blood sample, or other biological samples. Sample preparation may include adding an anti-coagulant or other ingredients to a sample. Sample preparation may also include purification of a sample. In embodiments, all sample processing, preparation, or assay actions or steps are performed by a single device. In embodiments, all sample processing, preparation, or assay actions or steps are performed within a housing of a single device. In embodiments, most sample processing, preparation, or assay actions or steps are performed by a single device, and may be performed within a housing of a single device. In embodiments, many sample processing, preparation, or assay actions or steps are performed by a single device, and may be performed within a housing of a single device. In embodiments, sample processing, preparation, or assay actions or steps may be performed by more than one device.

A sample processing device may be configured to run one or more assays on a sample, and to obtain data from the sample. A sample processing device may perform methods provided herein, as well as additional assays. An assay may include one or more physical or chemical treatments, and may include running one or more chemical or physical reactions. A sample processing device may be configured to perform one, two or more assays on a small sample of bodily fluid. One or more chemical reaction may take place on a sample having a volume, as described elsewhere herein. For example one or more chemical reaction may take place in a pill having less than femtoliter volumes. In an instance, the sample collection unit is configured to receive a volume of the bodily fluid sample equivalent to a single drop or less of blood or interstitial fluid. In embodiments, the volume of a sample may be a small volume, where a small volume may be a volume that is less than about 1000 μL, or less than about 500 μL, or less than about 250 μL, or less than about 150 μL, or less than about 100 μL, or less than about 75 μL, or less than about 50 μL, or less than about 40 μL, or less than about 20 μL, or less than about 10 μL, less than about 5 μL, less than about 1 μL, less than about 0.5 μL, less than about 0.1 μL, or other small volume. In embodiments, all sample assay actions or steps are performed on a single sample. In embodiments, all sample assay actions or steps are performed by a single device. In embodiments, all sample assay actions or steps are performed within a housing of a single device. In embodiments, most sample assay actions or steps are performed by a single device, and may be performed within a housing of a single device. In embodiments, many sample assay actions or steps are performed by a single device, and may be performed within a housing of a single device. In embodiments, sample processing, preparation, or assay actions or steps may be performed by more than one device.

A sample processing device may be configured to perform a plurality of assays on a sample. In some embodiments, a sample processing device may be configured to perform a method provided herein and one, two, or more additional assays. In embodiments, a sample processing device may be configured to perform a plurality of assays on a single sample. In embodiments, a sample processing device may be configured to perform a plurality of assays on a single sample, where the sample is a small sample. For example, a small sample may have a sample volume that is a small volume of less than about 1000 μL, or less than about 500 μL, or less than about 250 μL, or less than about 150 μL, or less than about 100 μL, or less than about 75 μL, or less than about 50 μL, or less than about 40 μL, or less than about 20 μL, or less than about 10 μL, less than about 5 μL, less than about 1 μL, less than about 0.5 μL, less than about 0.1 μL, or other small volume. A sample processing device may be capable of performing multiplexed assays on a single sample. A plurality of assays may be run simultaneously; may be run sequentially; or some assays may be run simultaneously while others are run sequentially. One or more control assays and/or calibrators (e.g., including a configuration with a control of a calibrator for the assay/tests) can also be incorporated into the device; control assays and assay on calibrators may be performed simultaneously with assays performed on a sample, or may be performed before or after assays performed on a sample, or any combination thereof. In embodiments, all sample assay actions or steps are performed by a single device. In embodiments, all of a plurality of assay actions or steps are performed within a housing of a single device. In embodiments, most sample assay actions or steps, of a plurality of assays, are performed by a single device, and may be performed within a housing of a single device. In embodiments, many sample assay actions or steps, of a plurality of assays, are performed by a single device, and may be performed within a housing of a single device. In embodiments, sample processing, preparation, or assay actions or steps may be performed by more than one device.

In embodiments, all of a plurality of assays may be performed in a short time period. In embodiments, such a short time period comprises less than about three hours, or less than about two hours, or less than about one hour, or less than about 40 minutes, or less than about 30 minutes, or less than about 25 minutes, or less than about 20 minutes, or less than about 15 minutes, or less than about 10 minutes, or less than about 5 minutes, or less than about 4 minutes, or less than about 3 minutes, or less than about 2 minutes, or less than about 1 minute, or other short time period.

A sample processing device may be configured to detect one or more signals relating to the sample. A sample processing device may be configured to identify one or more properties of the sample. For instance, the sample processing device may be configured to detect the presence or concentration of one analyte (e.g. a target nucleic acid) or a plurality of analytes or a disease condition in the sample (e.g., in or through a bodily fluid, secretion, tissue, or other sample). Alternatively, the sample processing device may be configured to detect a signal or signals that may be analyzed to detect the presence or concentration of one or more analytes (which may be indicative of a disease condition) or a disease condition in the sample. The signals may be analyzed on board the device, or at another location. Running a clinical test may or may not include any analysis or comparison of data collected.

A chemical reaction or other processing step may be performed, with or without the sample. Examples of steps, tests, or assays that may be prepared or run by the device may include, but are not limited to immunoassay, nucleic acid assay (e.g. methods provided herein), receptor-based assay, cytometric assay, colorimetric assay, enzymatic assay, electrophoretic assay, electrochemical assay, spectroscopic assay, chromatographic assay, microscopic assay, topographic assay, calorimetric assay, turbidimetric assay, agglutination assay, radioisotope assay, viscometric assay, coagulation assay, clotting time assay, protein synthesis assay, histological assay, culture assay, osmolarity assay, and/or other types of assays, centrifugation, separation, filtration, dilution, enriching, purification, precipitation, pulverization, incubation, pipetting, transport, cell lysis, or other sample preparation action or steps, or combinations thereof. Steps, tests, or assays that may be prepared or run by the device may include imaging, including microscopy, cytometry, and other techniques preparing or utilizing images. Steps, tests, or assays that may be prepared or run by the device may further include an assessment of histology, morphology, kinematics, dynamics, and/or state of a sample, which may include such assessment for cells.

A device may be capable of performing all on-board steps (e.g., steps or actions performed by a single device) in a short amount of time. A device may be capable of performing all on-board steps on a single sample in a short amount of time. For example, from sample collection from a subject to transmitting data and/or to analysis may take about 3 hours or less, 2 hours or less, 1 hour or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 30 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 5 minutes or less, 4 minutes or less, 3 minutes or less, 2 minutes or less, or 1 minute or less. The amount of time from accepting a sample within the device to transmitting data and/or to analysis from the device regarding such a sample may depend on the type or number of steps, tests, or assays performed on the sample. The amount of time from accepting a sample within the device to transmitting data and/or to analysis from the device regarding such a sample may take about 3 hours or less, 2 hours or less, 1 hour or less, 50 minutes or less, 45 minutes or less, 40 minutes or less, 30 minutes or less, 20 minutes or less, 15 minutes or less, 10 minutes or less, 5 minutes or less, 4 minutes or less, 3 minutes or less, 2 minutes or less, or 1 minute or less.

A device may be configured to prepare a sample for disposal, or to dispose of a sample, such as a biological sample, following processing or assaying of a sample.

In embodiments, a sample processing device may be configured to transmit data obtained from a sample. In embodiments, a sample processing device may be configured to communicate over a network. A sample processing device may include a communication module that may interface with the network. A sample processing device may be connected to the network via a wired connection or wirelessly. The network may be a local area network (LAN) or a wide area network (WAN) such as the Internet. In some embodiments, the network may be a personal area network. The network may include the cloud. The sample processing device may be connected to the network without requiring an intermediary device, or an intermediary device may be required to connect a sample processing device to a network. A sample processing device may communicate over a network with another device, which may be any type of networked device, including but not limited to a personal computer, server computer, or laptop computer; personal digital assistants (PDAs) such as a Windows CE device; phones such as cellular phones, smartphones (e.g., iPhone, Android, Blackberry, etc.), or location-aware portable phones (such as GPS); a roaming device, such as a network-connected roaming device; a wireless device such as a wireless email device or other device capable of communicating wireless with a computer network; or any other type of network device that may communicate possibly over a network and handle electronic transactions. Such communication may include providing data to a cloud computing infrastructure or any other type of data storage infrastructure which may be accessed by other devices.

A sample processing device may provide data regarding a sample to, e.g., a health care professional, a health care professional location, such as a laboratory, or an affiliate thereof. One or more of a laboratory, health care professional, or subject may have a network device able to receive or access data provided by the sample processing device. A sample processing device may be configured to provide data regarding a sample to a database. A sample processing device may be configured to provide data regarding a sample to an electronic medical records system, to a laboratory information system, to a laboratory automation system, or other system or software. A sample processing device may provide data in the form of a report.

A laboratory, device, or other entity or software may perform analysis on data regarding a sample in real-time. A software system may perform chemical analysis and/or pathological analysis, or these could be distributed amongst combinations of lab, clinical, and specialty or expert personnel. Analysis may include qualitative and/or quantitative evaluation of a sample. Data analysis may include a subsequent qualitative and/or quantitative evaluation of a sample. Optionally, a report may be generated based on raw data, pre-processed data, or analyzed data. Such a report may be prepared so as to maintain confidentiality of the data obtained from the sample, the identity and other information regarding the subject from whom a sample was obtained, analysis of the data, and other confidential information. The report and/or the data may be transmitted to a health care professional. Data obtained by a sample processing device, or analysis of such data, or reports, may be provided to a database, an electronic medical records system, to a laboratory information system, to a laboratory automation system, or other system or software.

Description and disclosure of examples of reagents, assays, methods, kits, devices, and systems which may use, or be used with, methods, compositions, or other reagents disclosed herein may be found, for example, in U.S. Pat. No. 8,088,593; U.S. Pat. No. 8,380,541; U.S. patent application Ser. No. 13/769,798, filed Feb. 18, 2013; U.S. patent application Ser. No. 13/769,779, filed Feb. 18, 2013; U.S. patent application Ser. No. 13/244,947 filed Sep. 26, 2011; PCT/US2012/57155, filed Sep. 25, 2012; U.S. application Ser. No. 13/244,946, filed Sep. 26, 2011; U.S. patent application Ser. No. 13/244,949, filed Sep. 26, 2011; and U.S. Application Ser. No. 61/673,245, filed Sep. 26, 2011, the disclosures of which patents and patent applications are all hereby incorporated by reference in their entireties.

EXAMPLES

The following examples are offered for illustrative purposes only, and are not intended to limit the present disclosure in any way.

Example 1—Amplification of a Template Nucleic Acid with Primers of Variable Tail Region Length

A method as provided herein was used to amplify a target nucleic acid. Reactions were prepared to assay for target nucleic acid from T124A1, which is a 464 nucleotide RNA molecule from an influenza A virus hemagglutinin (HA) gene, strain H3N2. 12 variants of a first primer (“P1”) and 12 variants of a second primer (“P2”) were prepared. The sequence of all of the primer variants is provided in FIG. 2A. All of the primers contained a template-binding region 15 nucleotides in length. The sequence of the template-binding region of all of the variants of the first primer was: CAAACCGTACCAACC (in the 5′-3′ direction). The sequence of the template-binding region of all of the variants of the second primer was: ATGCGGAATGTACC (in the 5′-3′ direction). The different primer variants contained tail regions ranging from 8 to 22 nucleotides in length, specifically 8, 9, 10, 11, 12, 13, 14, 15, 16, 18, 20, or 22 nucleotides in length. The tail region of the first primer had a base sequence of: CGCCGGATGGCTCTTGGGAAAC (in the 5′-3′ direction). The base sequence is 22 nucleotides in length; the shorter tail regions of the first primer have the same sequence, minus the appropriate number of nucleotides from the 5′ end of the tail region (e.g. the primer with the 18 nucleotide length tail region has a tail region with the same sequence as the base sequence, minus the first 4 nucleotides (CGCC) of the base sequence). The tail region of the second primer had a base sequence of: GTTTCCCAAGAGCCATCCGGCG (in the 5′-3′ direction). The base sequence is 22 nucleotides in length; the shorter tail regions of the first primer have the same sequence, minus the appropriate number of nucleotides from the 5′ end of the tail region (e.g. the primer with the 18 nucleotide length tail region has a tail region with the same sequence as the base sequence, minus the first 4 nucleotides (GTTT) of the base sequence).

150 microliter reaction mixtures were prepared, each containing: 50 mM potassium acetate, 20 mM Tris-acetate, pH 7.9, 10 mM magnesium acetate, 1 mM DTT, 30 μg bovine serum albumin (BSA), 0.8 M betaine, 1.4 mM each of dATP, dTTP, dGTP, and dCTP, 0.4×SYTO® 59 (Life Technologies), 0.8 units/μl Bst DNA polymerase (New England BioLabs), 0.016 units/μl AMV reverse trancriptase enzyme (New England Biolabs), 1 unit/μl murine RNase inhibitor (New England Biolabs), 0.8 μM of a first primer variant, 0.8 μM of a second primer variant, and 100,000 copies T124A1 template per microliter, and incubated at 59 C for 100 minutes in a CFX 96 Touch instrument (Bio-Rad). The inflection points for the assays were determined using a single-threshold method with CFX Manager software (Bio-Rad), and are shown in FIG. 2B. The X-axis provides the length in nucleotides of the tail region of the first and second primer used in the reaction, and the Y-axis provides the inflection time (in minutes) of the assay. “Cq” refers to the quantification cycle value (time) of the inflection point. For each tail region nucleotide length, two adjacent bars are shown: the left bar is the inflection time for the reaction containing template, and the right bar is the inflection time for the reaction lacking template [“no template control” (“NTC”)]. As shown in FIG. 2B, under these reaction conditions, primers with tail regions of 8-15 nucleotides, and, more particularly, 8-11 nucleotides supported the fastest inflection times. The no template control reactions sometimes show an inflection time; this is due to background non-specific products that are formed over time.

Example 2—Amplification of a Template Nucleic Acids with Primers of Variable Tail Region Length and Variable Template-Binding Region Length

A method as provided herein was used to amplify a target nucleic acid. Reactions were prepared to assay for target nucleic acid from T124A1, as described above in Example 1. Two different groups of first primer and second primer pair sets were prepared. In the first group of primer pairs, each of the primers had a template binding region 20 nucleotides in length (the “20 nucleotide template binding region” group). In the second group of primer pairs, each of the primers had a template binding region 16 nucleotides in length (the “16 nucleotide template binding region” group). Within each group, first and second primer pair sets with 8 different tail region lengths were prepared: 7, 8, 9, 10, 11, 12, 14, and 16 nucleotides. FIG. 3 provides the nucleotide sequences of the different primer pair sets for the 16 nucleotide template binding region group (FIG. 3A) and the 20 nucleotide template binding region group (FIG. 3B). In FIGS. 3A and 3B, the “tail” sequence refers to the tail region, and the “primer” region refers to the template-binding region of the primer. The sequences of the primers are shown in the 5′-3′ direction.

110 microliter reaction mixtures were prepared, each containing: 50 mM potassium acetate, 20 mM Tris-acetate, pH 7.9, 10 mM magnesium acetate, 1 mM DTT, 30 μg bovine serum albumin (BSA), 0.8 M betaine, 1.4 mM each of dATP, dTTP, dGTP, and dCTP, 0.4×SYTO® 59 (Life Technologies), 0.8 units/μl Bst DNA polymerase (New England BioLabs), 0.016 units/μl AMV reverse trancriptase enzyme (New England Biolabs), 1 unit/μl murine RNase inhibitor (New England Biolabs), 0.8 μM of a first primer variant, 0.8 μM of a second primer variant, and 100,000 copies T124A1 template per microliter, and incubated at 56 C for 100 minutes in a CFX 96 Touch instrument (Bio-Rad). The inflection points for the assays are shown in FIGS. 3C (20 nucleotide template binding region group) and 3D (16 nucleotide template binding region group). In both FIGS. 3C and 3D, the X-axis provides the length in nucleotides of the tail region of the first and second primer used in the reaction, and the Y-axis provides the inflection time (in minutes) of the assay. For each tail region nucleotide length, two adjacent bars are shown: the left bar is the inflection time for the reaction containing template, and the right bar is the inflection time for the reaction lacking template. As shown in FIG. 3, under these reaction conditions, with shorter template binding regions and tail regions showed faster inflection times and greater separation between the inflection time of reactions containing template versus reactions without template.

Example 3—Amplification of a Template Nucleic Acid at Variable Temperatures

A method as provided herein was used to amplify a target nucleic acid. Reactions were prepared to assay for target nucleic acid from T124A1, as described above in Example 1. First primer “RLX0892” (sequence: 5′ TTGGGAAACCAAACCGTACCAACC 3′) and second primer “RLX0893” (sequence: 5′ GTTTCCCAAATGCGGAATGTACC 3′) were used to amplify T124A1. Both of these primers have a 9 nucleotide tail region and a 14 nucleotide template-binding region.

80 microliter reaction mixtures were prepared, each containing: 50 mM potassium acetate, 20 mM Tris-acetate, pH 7.9, 10 mM magnesium acetate, 1 mM DTT, 20 μg bovine serum albumin (BSA), 0.8 M betaine, 1.4 mM each of dATP, dTTP, dGTP, and dCTP, 0.4×SYTO® 59 (Life Technologies), 0.8 units/μl Bst DNA polymerase (New England BioLabs), 0.016 units/μl AMV reverse trancriptase enzyme (New England Biolabs), 1 unit/μl murine RNase inhibitor (New England Biolabs), 0.8 μM of first primer RLX0892, 0.8 μM of second primer RLX0893, and 10,000, 1,000, 100 or 0 copies T124A1 template per microliter, and incubated in triplicate at 52, 52.7, 54, 55.9, 58.4, 60.3, 61.4 or 62 C for 100 minutes in a CFX 96 Touch instrument (Bio-Rad). The inflection points for the assays are shown in FIG. 4. The X-axis provides the incubation temperature of the reaction, and the Y-axis provides the inflection time (in minutes) of the assay. For each temperature, 4 adjacent bars are shown, from left to right: 10,000 copies template/microliter, 1000 copies template/microliter, 100 copies template/microliter, or no template control. As shown in FIG. 4, under these reaction conditions, the assays effectively amplified the template at 1000 copies template/microliter across the full range of temperatures from 52-62 C, and at some temperatures, at concentrations of template at least as low as 100 copies template/microliter.

Example 4—Amplification of a Template Nucleic Acid in the Presence of Genomic DNA

A method as provided herein was used to amplify a target nucleic acid. Reactions were prepared to assay for target nucleic acid from T124A1 (described above) in the presence of human DNA. First primer “RLX0892” (described above) and second primer “RLX0893” (described above) were used to amplify T124A1.

160 microliter reaction mixtures were prepared, each containing: 50 mM potassium acetate, 20 mM Tris-acetate, pH 7.9, 10 mM magnesium acetate, 1 mM DTT, 20 μg bovine serum albumin (BSA), 0.8 M betaine, 1.4 mM each of dATP, dTTP, dGTP, and dCTP, 0.4×SYTO® 59 (Life Technologies), 0.8 units/μl Bst DNA polymerase (New England BioLabs), 0.016 units/μl AMV reverse trancriptase enzyme (New England Biolabs), 1 unit/μl murine RNase inhibitor (New England Biolabs), 0.8 μM of first primer RLX0892, 0.8 μM of second primer RLX0893, and 1,000, 100 or 0 copies T124A1 template per microliter, and 0, 1, 2.5, 5, or nanograms human genomic DNA, and incubated at 56 C for 100 minutes in a CFX 96 Touch instrument (Bio-Rad). The inflection points for the assays are shown in FIG. 5. The X-axis provides the quantity of human genomic DNA (“hDNA”) in the reaction, and the Y-axis provides the inflection time (in minutes) of the assay. For each quantity of hDNA, 3 adjacent bars are shown, from left to right: 1000 copies template/microliter, 100 copies template/microliter, or no template. As shown in FIG. 5, under these reaction conditions, the assays effectively amplified the template at 1000 copies template/microliter in the presence of at least 10 ng hDNA. Also, the addition of hDNA the reactions caused only a relatively small decrease in NTC inflection times, even at concentrations of 5 or 10 ng hDNA.

Example 5—Amplification of a Template Nucleic Acid from a Viral Lysate Eluate

A method as provided herein was used to amplify a target nucleic acid from two different samples containing the target. Target nucleic acid from T124A1 was prepared in two samples: 1) a sample containing isolated T124A1 RNA molecule (as in Example 1), and 2) a FluA viral lysates sample. T124A1 is a gene in FluA, and therefore is expected to be present in a FluA viral lysate. FluA viral lysate was prepared with a Chemagic viral DNA/RNA kit (PerkinElmer), according to the manufacturer's instructions. The concentration of T124A1 in the two different samples was quantified by qPCR, and the samples were diluted to normalize the concentration of T124A1 in the samples. First primer “RLX0892” and second primer “RLX0893” were used to amplify T124A1.

25 microliter reaction mixtures were prepared, each containing: 50 mM potassium acetate, 20 mM Tris-acetate, pH 7.9, 10 mM magnesium acetate, 1 mM DTT, 20 μg bovine serum albumin (BSA), 0.8 M betaine, 1.4 mM each of dATP, dTTP, dGTP, and dCTP, 0.4×SYTO® 59 (Life Technologies), 0.8 units/μl Bst DNA polymerase (New England BioLabs), 0.016 units/μl AMV reverse trancriptase enzyme (New England Biolabs), 1 unit/μl murine RNase inhibitor (New England Biolabs), 0.8 μM of first primer RLX0892, 0.8 μM of second primer RLX0893, and 10,000, 1000 or 0 copies T124A1 template per microliter, and incubated at 56 C for 100 minutes in a CFX 96 Touch instrument (Bio-Rad). The inflection points for the assays are shown in FIG. 6. The X-axis provides the copies of template/microliter in the reaction, and the Y-axis provides the inflection time (in minutes) of the assay. For each quantity of copies of template/microliter, 2 adjacent bars are shown, from left to right: isolated T124A1, and FluA viral lysate. The inflection point for the NTC is also shown. As shown in FIG. 6, under these reaction conditions, the assays effectively amplified both isolated T124A1 template, as well as T124A1 template in a FluA viral lysate.

Example 6—Amplification of a Template Nucleic Acid

A method as provided herein was used to amplify a target nucleic acid. Reactions were prepared to assay for target nucleic acid from T129D1, which is a 298 nucleotide RNA molecule from an influenza B virus hemagglutinin (HA) gene. First primer “A8” (nucleotide sequence: 5′ TCTTGAGAGAACCCACTAAC 3′) and second primer “B8” (nucleotide sequence: 5′ TCTCAAGAATTTGGTCTTCC 3′) were used to amplify T129D1. In both of these primers, the first 8 nucleotides (from the 5′ terminus) are the tail region, and the last 12 nucleotides are the template-binding region. Together, these primers are targeted to amplify a 54 nucleotide sequence of the T129D1 gene.

A 100 microliter reaction mixture was prepared, containing: 50 mM potassium acetate, 20 mM Tris-acetate, pH 7.9, 10 mM magnesium acetate, 1 mM DTT, 20 μg bovine serum albumin (BSA), 0.8 M betaine, 1.4 mM each of dATP, dTTP, dGTP, and dCTP, 0.4×SYTO® 59 (Life Technologies), 0.8 units/μl Bst DNA polymerase (New England BioLabs), 0.016 units/μl AMV reverse trancriptase enzyme (New England Biolabs), 1 unit/μl murine RNase inhibitor (New England Biolabs), 0.8 μM of first primer A8, 0.8 μM of second primer B8, and 100,000 T129D1 template per microliter, and incubated at 58 C for 100 minutes in a CFX 96 Touch instrument (Bio-Rad). After the 100 minutes, a sample was taken from the reaction, and ligated into cloning vectors. Vectors containing reaction products were sequenced using vector-specific primers, directed to toward the cloning site. The results from multiple example sequencing reactions are shown in FIG. 7. The sequencing results show that concatemers having the expected structure are formed. Specifically, in these examples, in a single strand of the reaction product, multiple copies of the targeted 54 nucleotide sequence from the T129D1 gene are present, separated by the sequence of the tail region of the A8 primer (5′ TCTTGAGA 3′).

While preferred embodiments of the present invention have been shown and described herein, it will be obvious to those skilled in the art that such embodiments are provided by way of example only. The foregoing description is not intended to be exhaustive or to limit the invention to the precise embodiments disclosed, and other modifications and variations may be possible in light of the above teachings without departing from the invention. Any feature, whether preferred or not, may be combined with any other feature, whether preferred or not. It should also be understood that while the invention provided herein has been described herein using a limited number of terms and phrases for purposes of expediency, the invention could also be described using other terms and phrases not provided herein which also accurately describe the invention. The appended claims are not to be interpreted as including means-plus-function limitations, unless such a limitation is explicitly recited in a given claim using the phrase “means for.” It should be understood that as used in the description herein and throughout the claims that follow, the meaning of “a,” “an,” and “the” includes plural reference unless the context clearly dictates otherwise. For example, a reference to “an assay” may refer to a single assay or multiple assays. Also, as used in the description herein and throughout the claims that follow, the meaning of “in” includes “in” and “on” unless the context clearly dictates otherwise. As used in the description herein and through the claims that follow, a first object described as containing “at least a portion” of a second object may contain the full amount of/the complete second object. As used in the description herein and throughout the claims that follow, the terms “comprise”, “include”, and “contain” and related tenses are inclusive and open-ended, and do not exclude additional, unrecited elements or method steps. Finally, as used in the description herein and throughout the claims that follow, the meaning of “or” includes both the conjunctive and disjunctive unless the context expressly dictates otherwise. Thus, the term “or” includes “and/or” unless the context expressly dictates otherwise.

This document contains material subject to copyright protection. The copyright owner (Applicant herein) has no objection to facsimile reproduction by anyone of the patent documents or the patent disclosure, as they appear in the US Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. The following notice shall apply: Copyright 2013 Theranos, Inc. 

We claim:
 1. A method for generating a concatemer comprising two or more copies of a double-stranded nucleic acid template, the method comprising: (A) treating a primary double-stranded nucleic acid comprising the double-stranded nucleic acid template with a first copy of a first primer and a polymerase under conditions such that an extension product of the first copy of the first primer is synthesized which is annealed to a first strand of the double-stranded nucleic acid template, wherein the first primer comprises a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and the template-binding region of the first copy of the first primer anneals to the first strand of the double-stranded nucleic acid template, (B) treating the extension product of the first copy of the first primer of step (A) with a second primer and a polymerase under conditions such that an extension product of the second primer is synthesized which is annealed to the extension product of the first copy of the first primer of step (A), wherein the second primer comprises a 5′ terminal nucleotide, a 3′ terminal nucleotide, and two regions: (i) a tail region comprising (a) the 5′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is downstream from the 5′ terminal nucleotide (c) a middle section between the 5′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, and (ii) a template-binding region comprising (a) the 3′ terminal nucleotide of the primer (b) an innermost nucleotide, wherein the innermost nucleotide is upstream from the 3′ terminal nucleotide (c) a middle section between the 3′ terminal nucleotide and the innermost nucleotide, comprising one or more nucleotides, the tail region of the second primer contains a nucleotide sequence which is complementary to the nucleotide sequence of the tail region of the first primer if the sequences of the first primer and second primer are aligned such that the 5′ terminal nucleotide of the second primer is aligned with the innermost nucleotide of the tail region of the first primer and the 5′ terminal nucleotide of the first primer is aligned with the innermost nucleotide of the tail region of the second primer, the template-binding region of the second primer anneals to the extension product of the first copy of the first primer of step (A), and the extension product of the second primer contains a 5′ terminal nucleotide, a 3′ terminal nucleotide, and a 3′ terminal region comprising the 3′ terminal nucleotide, wherein the 3′ terminal region contains the same nucleotide sequence as the nucleotide sequence of the tail region of the second primer read in the 5′ to 3′ direction, (C) treating the extension product of the second primer of step (B) with a second copy of the first primer and a polymerase under conditions such that an extension product of the second copy of the first primer is synthesized which is annealed to the extension product of the second primer of step (B), to produce a first copy of a secondary nucleic acid comprising the extension product of the second primer of step (B) and the extension product of the second copy of the first primer, wherein the extension product of the second copy of the first primer contains a 5′ terminal nucleotide, a 3′ terminal nucleotide, and a 3′ terminal region comprising the 3′ terminal nucleotide, wherein the 3′ terminal region contains the same nucleotide sequence as the nucleotide sequence of the tail region of the first primer read in the 5′ to 3′ direction, (D) repeating steps (A)-(C) one or more addition times to generate at least a second copy of the secondary nucleic acid of step (C), (E) treating the first copy of the secondary nucleic acid of step (C) and the second copy of the secondary nucleic acid of step (D) under conditions such that the 3′ terminal region of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid anneals to the 3′ terminal region of the extension product of the second primer of the second copy of the secondary nucleic acid, to produce a cross-over structure comprising the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid and the extension product of the second primer of the second copy of the secondary nucleic acid, (F) treating the cross-over structure of step (E) with a polymerase under conditions such that an extension product of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid is synthesized and an extension product of the extension product of the second primer of the second copy of the secondary nucleic acid is synthesized, to produce a concatemer comprising two copies of the double-stranded nucleic acid template of step (A), wherein the concatemer comprises the extension product of the extension product of the second copy of the first primer of the first copy of the secondary nucleic acid and the extension product of the extension product of the second primer of the second copy of the secondary nucleic acid.
 2. The method of claim 1, wherein all steps of the method are performed at a temperature of no greater than 70 C.
 3. The method of claim 1, wherein two or more steps of the method are performed simultaneously.
 4. The method of claim 1, wherein the nucleic acid template is amplified at least 10-fold within 60 minutes of initiation of the method.
 5. The method of claim 1, further comprising treating one or more of the reaction components with a nucleic acid dye.
 6. The method of claim 1, wherein the tail region of each of the first primer and second primer comprises at least 6 nucleotides.
 7. The method of claim 1, wherein the tail region of each of the first primer and second primer comprises no more than 30 nucleotides.
 8. The method of claim 1, wherein the polymerase is a DNA polymerase.
 9. The method of claim 1, wherein all steps of the method are performed under isothermal conditions.
 10. The method of claim 9, wherein all steps of the method are performed at a temperature of no greater than 60° C.
 11. The method of claim 9, wherein all steps of the method are performed at a temperature of no greater than 50° C.
 12. The method of claim 9, wherein all steps of the method are performed at a temperature of no greater than 40° C.
 13. The method of claim 1, wherein the tail region of each of the first and second primer comprises at least 8 nucleotides.
 14. The method of claim 1, wherein the tail region of each of the first and second primer comprises at least 9 nucleotides.
 15. The method of claim 1, wherein the tail region of each of the first and second primer comprises at least 10 nucleotides.
 16. The method of claim 1, wherein the template binding region of each of the first and second primer comprises at least 6 nucleotides.
 17. The method of claim 1, wherein the template binding region of each of the first and second primer comprises at least 8 nucleotides.
 18. The method of claim 1, wherein the template binding region of each of the first and second primer comprises at least 9 nucleotides.
 19. The method of claim 1, wherein the template binding region of each of the first and second primer comprises at least 10 nucleotides.
 20. The method of claim 1, wherein the template binding region of each of the first and second primer comprises no more than 30 nucleotides. 